Add yamllint (#26965)

So that https://github.com/go-gitea/gitea/pull/26964 does not happen
again. Merge this after that PR. Config is based on
[node's](https://github.com/nodejs/node/blob/main/.yamllint.yaml).

---------

Co-authored-by: techknowlogick <techknowlogick@gitea.com>

.github/workflows/files-changed.yml

@@ -17,6 +17,8 @@ on:
         value: ${{ jobs.detect.outputs.docker }}
       swagger:
         value: ${{ jobs.detect.outputs.swagger }}
+      yaml:
+        value: ${{ jobs.detect.outputs.yaml }}
 
 jobs:
   detect:
@@ -30,6 +32,7 @@ jobs:
       templates: ${{ steps.changes.outputs.templates }}
       docker: ${{ steps.changes.outputs.docker }}
       swagger: ${{ steps.changes.outputs.swagger }}
+      yaml: ${{ steps.changes.outputs.yaml }}
     steps:
       - uses: actions/checkout@v3
       - uses: dorny/paths-filter@v2
@@ -82,3 +85,8 @@ jobs:
               - "package.json"
               - "package-lock.json"
               - ".spectral.yaml"
+
+            yaml:
+              - "**/*.yml"
+              - "**/*.yaml"
+              - ".yamllint.yaml"