[buildbot] ci: add support for testing PR containers

[LEDE Commits]

ynezz pushed a commit to buildbot.git, branch main:
https://git.openwrt.org/93918cc2e2257ae8838166d2baad30617295df4e

commit 93918cc2e2257ae8838166d2baad30617295df4e
Author: Petr Štetiar <ynezz at true.cz>
AuthorDate: Sun Jan 11 10:25:00 2026 +0100

    ci: add support for testing PR containers
    
    Enable PR container publishing to GHCR with pr-<number> tags so that
    containers can be manually tested before merging. Add cleanup workflow
    to automatically delete PR containers when the PR is closed.
    
    Signed-off-by: Petr Štetiar <ynezz at true.cz>
---
 .github/workflows/build-push.yml            | 21 +++++++++++++++++--
 .github/workflows/cleanup-pr-containers.yml | 32 +++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/build-push.yml b/.github/workflows/build-push.yml
index 16b66e0..31f3920 100644
--- a/.github/workflows/build-push.yml
+++ b/.github/workflows/build-push.yml
@@ -6,6 +6,12 @@ on:
     tags:
       - 'v*'
   pull_request:
+  workflow_dispatch:
+    inputs:
+      pr_number:
+        description: 'PR number to build and push container for'
+        required: true
+        type: number
 
 env:
   BUILDBOT_VERSION: 3.11.8
@@ -28,6 +34,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout at v5
+        with:
+          ref: ${{ github.event_name == 'workflow_dispatch' && format('refs/pull/{0}/merge', inputs.pr_number) || '' }}
 
       - uses: actions/setup-python at v5
         with:
@@ -64,6 +72,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout at v5
+        with:
+          ref: ${{ github.event_name == 'workflow_dispatch' && format('refs/pull/{0}/merge', inputs.pr_number) || '' }}
 
       - name: Environment variables
         run: |
@@ -88,7 +98,7 @@ jobs:
 
   deploy:
     name: Push Container
-    if: github.event_name != 'pull_request' || github.repository_owner != 'openwrt'
+    if: github.event_name != 'pull_request'
     runs-on: ubuntu-latest
     needs: build-test
 
@@ -106,6 +116,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout at v5
+        with:
+          ref: ${{ github.event_name == 'workflow_dispatch' && format('refs/pull/{0}/merge', inputs.pr_number) || '' }}
 
       - name: Environment variables
         run: |
@@ -115,7 +127,12 @@ jobs:
         id: meta
         uses: docker/metadata-action at v5
         with:
-          images: name=ghcr.io/${{ github.repository }}/build${{ matrix.container_flavor }}-v${{ env.BUILDBOT_VERSION }}
+          images: ghcr.io/${{ github.repository }}/build${{ matrix.container_flavor }}-v${{ env.BUILDBOT_VERSION }}
+          tags: |
+            type=raw,value=pr-${{ inputs.pr_number }},enable=${{ github.event_name == 'workflow_dispatch' }}
+            type=ref,event=branch
+            type=sha,prefix=sha-,enable=${{ github.event_name != 'workflow_dispatch' }}
+            type=semver,pattern={{version}}
 
       - name: Login to GitHub Container Registry
         uses: docker/login-action at v3
diff --git a/.github/workflows/cleanup-pr-containers.yml b/.github/workflows/cleanup-pr-containers.yml
new file mode 100644
index 0000000..073b4b8
--- /dev/null
+++ b/.github/workflows/cleanup-pr-containers.yml
@@ -0,0 +1,32 @@
+name: Cleanup PR Containers
+
+on:
+  pull_request:
+    types: [closed]
+
+env:
+  BUILDBOT_VERSION: 3.11.8
+
+jobs:
+  cleanup:
+    name: Delete PR container images
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+
+    strategy:
+      matrix:
+        container_flavor:
+          - master
+          - worker
+
+    steps:
+      - name: Delete PR container image
+        uses: actions/delete-package-versions at v5
+        with:
+          package-name: buildbot/build${{ matrix.container_flavor }}-v${{ env.BUILDBOT_VERSION }}
+          package-type: container
+          delete-only-pre-release-versions: false
+          min-versions-to-keep: 0
+          delete-only-untagged-versions: false
+          version-pattern: pr-${{ github.event.pull_request.number }}