GH Actions: add Yamllint to QA basics

... to loosely safeguard valid and consistent yaml files.

Includes adding a configuration file which loosens up the `default` ruleset to a degree I'm comfortable with.

Ref: https://yamllint.readthedocs.io/

Author: jrfnl

.gitattributes

@@ -11,6 +11,7 @@
 /.markdownlint-cli2.yaml export-ignore
 /.remarkignore           export-ignore
 /.remarkrc               export-ignore
+/.yamllint.yml           export-ignore
 /phpcs.xml.dist          export-ignore
 /phpstan.neon.dist       export-ignore
 /phpunit.xml.dist        export-ignore

.github/workflows/cs.yml

@@ -150,3 +150,9 @@ jobs:
   remark:
     name: 'QA Markdown'
     uses: PHPCSStandards/.github/.github/workflows/reusable-remark.yml@main
+
+  yamllint:
+    name: 'Lint Yaml'
+    uses: PHPCSStandards/.github/.github/workflows/reusable-yamllint.yml@main
+    with:
+      strict: true

.yamllint.yml

@@ -0,0 +1,23 @@
+# Details on the default config:
+# https://yamllint.readthedocs.io/en/stable/configuration.html#default-configuration
+extends: default
+
+yaml-files:
+  - '*.yaml'
+  - '*.yml'
+  - '.yamllint'
+  - 'phpstan.neon*'
+
+# Rule documentation: https://yamllint.readthedocs.io/en/stable/rules.html
+rules:
+  colons:
+    max-spaces-after: -1  # Disabled to allow aligning of values.
+  comments:
+    min-spaces-from-content: 1
+  comments-indentation: {}
+  document-start:
+    present: false
+  line-length:
+    max: 145
+  truthy:
+    allowed-values: ["true", "false", "on", "off"]