Test only with JRuby 9.2.21.0 in CI (disable 9.2.8.0)

**What does this PR do?**:

This PR disables testing of JRuby 9.2.8.0 in CI, as well as
appraisal generation for it (as well as removes the existing
appraisals).

**Motivation**:

Maintaining JRuby 9.2.8.0 working has been quite a burden: this version
has many, many, many known issues -- you will notice that there have
been **13** other bugfix releases on top of it; latest JRuby is
9.2.31.0.

Some examples of PRs where this JRuby version caused toil are
 #2565, #2558, #2448, #2412, #1869, etc

We've decided to stop running it in CI for now, and plan to evaluate
if we should remove it entirely from our test harness.

We recommend that all our customers use JRuby 9.2.21.0, and also
recommend evaluating the move to JRuby 9.3, as the JRuby developers have
marked JRuby 9.2 as end-of-life:
<https://twitter.com/jruby/status/1611063274459566106>.

**Additional Notes**:

I didn't have to remove the appraisal gemfiles from the tree, but
since I disabled the tasks that automatically keep them up-to-date,
they wouldn't be maintained anyway.

If/when we do want to revert this change, we should regenerate them using
the usual rake tasks.

**How to test the change?**:

Validate that CI is green and that the JRuby 9.2.8.0 configuration is
not shown there.

.circleci/config.yml

@@ -538,11 +538,12 @@ job_configuration:
     image: ghcr.io/datadog/dd-trace-rb/ruby:3.2.0-dd
     resource_class_to_use: medium+
     # ADD NEW RUBIES HERE
-  - &config-jruby-9_2_8_0 # Test with older 9.2 release because 9.2.9.0 changed behavior, see https://github.com/DataDog/dd-trace-rb/pull/1409
-    <<: *filters_all_branches_and_tags
-    ruby_version: 'jruby-9.2.8.0'
-    image: ghcr.io/datadog/dd-trace-rb/jruby:9.2.8.0-dd
-    resource_class_to_use: medium+
+  # TODO: Disabled for possible removal
+  # - &config-jruby-9_2_8_0 # Test with older 9.2 release because 9.2.9.0 changed behavior, see https://github.com/DataDog/dd-trace-rb/pull/1409
+  #   <<: *filters_all_branches_and_tags
+  #   ruby_version: 'jruby-9.2.8.0'
+  #   image: ghcr.io/datadog/dd-trace-rb/jruby:9.2.8.0-dd
+  #   resource_class_to_use: medium+
   - &config-jruby-9_2 # More recent release of 9.2
     <<: *filters_all_branches_and_tags
     ruby_version: 'jruby-9.2.21.0'
@@ -584,7 +585,8 @@ workflows:
             # TODO: Re-enable once 3.2 testing is green!
             #- test-3.2
             # ADD NEW RUBIES HERE
-            - test-jruby-9.2.8.0
+            # TODO: Disabled for possible removal
+            #- test-jruby-9.2.8.0
             - test-jruby-9.2
             - test-jruby-9.3
       - orb/changelog:
@@ -736,14 +738,15 @@ workflows:
       #     requires:
       #       - build-3.2
       # ADD NEW RUBIES HERE
-      - orb/build:
-          <<: *config-jruby-9_2_8_0
-          name: build-jruby-9.2.8.0
-      - orb/test:
-          <<: *config-jruby-9_2_8_0
-          name: test-jruby-9.2.8.0
-          requires:
-            - build-jruby-9.2.8.0
+      # TODO: Disabled for possible removal
+      # - orb/build:
+      #     <<: *config-jruby-9_2_8_0
+      #     name: build-jruby-9.2.8.0
+      # - orb/test:
+      #     <<: *config-jruby-9_2_8_0
+      #     name: test-jruby-9.2.8.0
+      #     requires:
+      #       - build-jruby-9.2.8.0
       - orb/build:
           <<: *config-jruby-9_2
           name: build-jruby-9.2
@@ -778,7 +781,8 @@ workflows:
             # TODO: Re-enable once 3.2 testing is green!
             #- test-3.2
             # ADD NEW RUBIES HERE
-            - test-jruby-9.2.8.0
+            # TODO: Disabled for possible removal
+            # - test-jruby-9.2.8.0
             - test-jruby-9.2
             - test-jruby-9.3
       - "deploy release":
@@ -798,7 +802,8 @@ workflows:
             # TODO: Re-enable once 3.2 testing is green!
             #- test-3.2
             # ADD NEW RUBIES HERE
-            - test-jruby-9.2.8.0
+            # TODO: Disabled for possible removal
+            # - test-jruby-9.2.8.0
             - test-jruby-9.2
             - test-jruby-9.3
   # This workflow runs the same `build` and `test` jobs as above on a schedule.
@@ -962,15 +967,16 @@ workflows:
       #     requires:
       #       - build-3.2
       # ADD NEW RUBIES HERE
-      - orb/build:
-          <<: *config-jruby-9_2_8_0
-          name: build-jruby-9.2.8.0
-          edge: true
-      - orb/test:
-          <<: *config-jruby-9_2_8_0
-          name: test-jruby-9.2.8.0
-          requires:
-            - build-jruby-9.2.8.0
+      # TODO: Disabled for possible removal
+      # - orb/build:
+      #     <<: *config-jruby-9_2_8_0
+      #     name: build-jruby-9.2.8.0
+      #     edge: true
+      # - orb/test:
+      #     <<: *config-jruby-9_2_8_0
+      #     name: test-jruby-9.2.8.0
+      #     requires:
+      #       - build-jruby-9.2.8.0
       - orb/build:
           <<: *config-jruby-9_2
           name: build-jruby-9.2

.github/workflows/build-ruby.yml

@@ -54,9 +54,10 @@ jobs:
           - engine: jruby
             version: 9.2.21.0
             dockerfile: Dockerfile-jruby-9.2.21.0
-          - engine: jruby
-            version: 9.2.8.0
-            dockerfile: Dockerfile-jruby-9.2.8.0
+          # TODO: Disabled for possible removal
+          # - engine: jruby
+          #   version: 9.2.8.0
+          #   dockerfile: Dockerfile-jruby-9.2.8.0
           - engine: jruby
             version: 9.3.9.0
             dockerfile: Dockerfile-jruby-9.3.9.0