Implement merge_group trigger and concurrency control

- Add merge_group event to oxipng.yml and docker.yml for native
  Merge Queue support.
- Implement concurrency groups with cancel-in-progress: true to
  terminate obsolete builds on new pushes.
- Remove explicit pull_request types to allow default triggers
  (including reopened).

.github/workflows/deploy.yml

@@ -5,6 +5,10 @@ on:
     tags:
       - "v*.*.*"
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 permissions:
   actions: read
   contents: write

.github/workflows/docker.yml

@@ -6,9 +6,7 @@ on:
     tags:
       - 'v*.*.*'
   pull_request:
-    types:
-      - opened
-      - synchronize
+  merge_group:
   workflow_dispatch:
     inputs:
       use_cache:
@@ -17,6 +15,10 @@ on:
         type: boolean
         default: true
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build:
     uses: docker/github-builder/.github/workflows/build.yml@v1

.github/workflows/oxipng.yml

@@ -3,11 +3,13 @@ name: oxipng
 on:
   push:
   pull_request:
-    types:
-      - opened
-      - synchronize
+  merge_group:
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   ci:
     name: CI