Only run docker-dryrun when necessary (#25329)

`docker-dryrun` runs on almost any PR, which is a huge waste of CI
resources. Run it only when the Dockerfiles change and also add a step
that verifies the rootless file.

---------

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

.github/workflows/files-changed.yml

@@ -4,24 +4,20 @@ on:
   workflow_call:
     outputs:
       backend:
-        description: "whether backend files changed"
         value: ${{ jobs.detect.outputs.backend }}
       frontend:
-        description: "whether frontend files changed"
         value: ${{ jobs.detect.outputs.frontend }}
       docs:
-        description: "whether docs files changed"
         value: ${{ jobs.detect.outputs.docs }}
       actions:
-        description: "whether actions files changed"
         value: ${{ jobs.detect.outputs.actions }}
       templates:
-        description: "whether templates files changed"
         value: ${{ jobs.detect.outputs.templates }}
+      docker:
+        value: ${{ jobs.detect.outputs.docker }}
 
 jobs:
   detect:
-    name: detect which files changed
     runs-on: ubuntu-latest
     timeout-minutes: 3
     # Map a step output to a job output
@@ -31,6 +27,7 @@ jobs:
       docs: ${{ steps.changes.outputs.docs }}
       actions: ${{ steps.changes.outputs.actions }}
       templates: ${{ steps.changes.outputs.templates }}
+      docker: ${{ steps.changes.outputs.docker }}
     steps:
       - uses: actions/checkout@v3
       - uses: dorny/paths-filter@v2
@@ -59,3 +56,7 @@ jobs:
             templates:
               - "templates/**/*.tmpl"
               - "poetry.lock"
+            docker:
+              - "Dockerfile"
+              - "Dockerfile.rootless"
+              - "docker/**"