Add YAML linting for golangci-lint config files

[atc0005]

The https://marketplace.visualstudio.com/items?itemName=redhat.vscode-yaml extension might be a resource that can be leveraged here.

[atc0005]

https://github.com/adrienverge/yamllint seems like it might do the job.

A recent enough version is available for installation via apt repos, or via pip for the latest version.

[atc0005]

$ docker run -it --rm -v $PWD:$PWD -w $PWD ghcr.io/atc0005/go-ci:go-ci-stable
root@a5d5a7803615:/home/ubuntu/Desktop/go-ci# ls -la
total 116
drwxrwxr-x 8 1000 1000  4096 Jun 19 13:48 .
drwxr-xr-x 3 root root  4096 Jun 20 10:22 ..
drwxrwxr-x 8 1000 1000  4096 Jun 20 10:11 .git
drwxrwxr-x 3 1000 1000  4096 Apr 25 10:07 .github
-rw-rw-r-- 1 1000 1000   446 Nov 29  2020 .gitignore
-rw-rw-r-- 1 1000 1000   676 Jun 19 12:46 .markdownlint.yml
-rw-rw-r-- 1 1000 1000 41928 Jun  2 11:48 CHANGELOG.md
-rw-rw-r-- 1 1000 1000  1070 Jul 30  2020 LICENSE
-rw-rw-r-- 1 1000 1000 17950 Jun 19 13:48 Makefile
-rw-rw-r-- 1 1000 1000  7892 Jun 19 13:48 README.md
drwxrwxr-x 2 1000 1000  4096 Jun 20 10:18 oldstable
drwxrwxr-x 5 1000 1000  4096 Jun 20 10:03 stable
drwxrwxr-x 2 1000 1000  4096 Jun 19 13:48 tools
drwxrwxr-x 2 1000 1000  4096 Jun 20 10:18 unstable
root@a5d5a7803615:/home/ubuntu/Desktop/go-ci# yamllint ./.markdownlint.yml 
./.markdownlint.yml
  13:1      warning  missing document start "---"  (document-start)

root@a5d5a7803615:/home/ubuntu/Desktop/go-ci# echo $?
0
root@a5d5a7803615:/home/ubuntu/Desktop/go-ci# yamllint ./stable/.golangci.yml 
./stable/.golangci.yml
  15:1      warning  missing document start "---"  (document-start)
  28:81     error    line too long (103 > 80 characters)  (line-length)
  86:81     error    line too long (82 > 80 characters)  (line-length)
  87:81     error    line too long (82 > 80 characters)  (line-length)

root@a5d5a7803615:/home/ubuntu/Desktop/go-ci# echo $?
1
root@a5d5a7803615:/home/ubuntu/Desktop/go-ci# yamllint ./stable/.golangci.yml 
./stable/.golangci.yml
  15:1      warning  missing document start "---"  (document-start)
  28:81     error    line too long (103 > 80 characters)  (line-length)

root@a5d5a7803615:/home/ubuntu/Desktop/go-ci# yamllint ./stable/.golangci.yml 
./stable/.golangci.yml
  15:1      warning  missing document start "---"  (document-start)

This is from a local build of what will be the v0.6.14 version of the go-ci-stable image.

The errors were resolved by fixing the line length:

diff --git a/stable/.golangci.yml b/stable/.golangci.yml
index 6c3a6b0..ab5ece2 100644
--- a/stable/.golangci.yml
+++ b/stable/.golangci.yml
@@ -25,7 +25,10 @@ issues:
 run:
   # Define the Go version limit.
   # Mainly related to generics support in go1.18.
-  # Default: use Go version from the go.mod file, fallback on the env var `GOVERSION`, fallback on 1.17
+  #
+  # Default: use Go version from the go.mod file, fallback on the env var
+  # `GOVERSION`, fallback on 1.17
+  #
   # https://github.com/golangci/golangci-lint/blob/master/.golangci.reference.yml
   go: "1.18"
 
@@ -83,9 +86,9 @@ linters-settings:
     enable-all: true
     disable:
       #
-      # Disable fieldalignment settings until the Go team offers more control over
-      # the types of checks provided by the fieldalignment linter or golangci-lint
-      # does so.
+      # Disable fieldalignment settings until the Go team offers more control
+      # over the types of checks provided by the fieldalignment linter or
+      # golangci-lint does so.
       #
       # See https://github.com/atc0005/go-ci/issues/302 for more information.
       #

[atc0005]

FWIW, yamllint doesn't flag this out of the box:

run:
  go: 1.18

whereas the https://marketplace.visualstudio.com/items?itemName=redhat.vscode-yaml VSCode extension does: