CI: delete docker-pr.yml

It needs QEMU, buildx and a ghcr.io login, none of which this forge provides.
Eureka's ruling, relayed in brief ratatoskr:follow_up:chat-s4646-4647: nothing here pulls container images (forge registry only, if ever).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.github/workflows/build-pull-request.yml

@@ -7,7 +7,7 @@ on:
 jobs:
   build-pull-request:
     name: Build pull request
-    runs-on: ubuntu-latest
+    runs-on: docker
     env:
       PR_NUMBER: ${{github.event.number}}
     steps:

.github/workflows/docker-pr.yml

@@ -1,62 +0,0 @@
-name: 'Docker check'
-
-on:
-  pull_request:
-    paths:
-      - 'Dockerfile'
-      - '.github/workflows/docker-pr.yml'
-
-jobs:
-  docker-build:
-    runs-on: ubuntu-latest
-    permissions:
-      contents: read
-      packages: write
-
-    steps:
-      - name: Checkout repository
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@1f40c72289eff860ee54a304f1438e3cff362e0a # v4.3.0
-        
-      - name: Set up Docker Buildx
-        uses: docker/setup-buildx-action@37fe631027851001ddb9b187196cc803df7f5f0e # v4.3.0
-
-      - name: Login to Docker Hub #Do not update this action from a outside PR
-        if: github.event.pull_request.head.repo.fork == false
-        uses: docker/login-action@dbcb813823bdd20940b903addbd779551569679f # v4.6.0
-        with:
-          username: ${{ secrets.DOCKER_USERNAME }}
-          password: ${{ secrets.DOCKER_PASSWORD }}
-        continue-on-error: true
-
-      - name: Login to the Github Container registry #Do not update this action from a outside PR
-        if: github.event.pull_request.head.repo.fork == false
-        uses: docker/login-action@dbcb813823bdd20940b903addbd779551569679f # v4.6.0
-        with:
-          registry: ghcr.io
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
-        continue-on-error: true
-
-      - name: Extract metadata (tags, labels) for Docker, GHCR
-        id: meta
-        uses: docker/metadata-action@dc802804100637a589fabce1cb79ff13a1411302 # v6.2.0
-        with:
-          images: |
-            ajbura/cinny
-            ghcr.io/${{ github.repository }}
-
-      - name: Build Docker image (no push)
-        uses: docker/build-push-action@53b7df96c91f9c12dcc8a07bcb9ccacbed38856a # v7.3.0
-        with:
-          context: .
-          platforms: linux/amd64
-          push: false
-          load: true
-          tags: ${{ steps.meta.outputs.tags }}
-          labels: ${{ steps.meta.outputs.labels }}
-
-      - name: Show Docker images
-        run: docker images

.github/workflows/lockfile.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   lockfile_changes:
-    runs-on: ubuntu-latest
+    runs-on: docker
     # Permission overwrite is required for Dependabot PRs, see "Common issues" below.
     permissions:
       contents: read

.github/workflows/rat-dev-preview.yml

@@ -7,7 +7,7 @@ on:
 jobs:
   build:
     name: Build dev preview
-    runs-on: ubuntu-latest
+    runs-on: docker
     timeout-minutes: 30
     steps:
       - name: Checkout repository