Configure GHA workflows for the 2-x-stable branch

It seems that the configurations

    on:
      - pull_request

and

    on:
      pull_request:

will only trigger a workflow run when the target branch is the repo's
default branch (but I could not find any documentation for it). Let's
see if an explicit branch name will make workflows run for our PRs.

.github/workflows/codespell.yml

@@ -1,6 +1,7 @@
 name: CodeSpell
 on:
-  - pull_request
+  pull_request:
+    branches: 2-x-stable
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true

.github/workflows/danger.yml

@@ -1,6 +1,7 @@
 name: Danger
 on:
-  - pull_request
+  pull_request:
+    branches: 2-x-stable
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true

.github/workflows/linting.yml

@@ -1,6 +1,7 @@
 name: Linting
 on:
-  - pull_request
+  pull_request:
+    branches: 2-x-stable
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true

.github/workflows/main.yml

@@ -2,9 +2,9 @@ name: CI
 
 on:
   pull_request:
+    branches: 2-x-stable
   push:
-    branches:
-      - master
+    branches: 2-x-stable
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}

.github/workflows/publish.yml

@@ -1,7 +1,7 @@
 name: Publish
 on:
   push:
-    branches: master
+    branches: 2-x-stable
     paths: lib/rubocop/rspec/version.rb
 jobs:
   publish: