fix(docker): Downgrade PHP from 8.5 to 8.3 and add PR CI check

PHP 8.5 is not officially released and causes docker-php-ext-install
to fail with "cp: can't stat 'modules/*'" error.

Changes:
- Revert to PHP 8.3-fpm-alpine (current stable LTS)
- Add pull_request trigger to docker-build workflow
- Use dorny/paths-filter to skip build when no Docker files changed
- Workflow can now be set as a required check (always runs, skips gracefully)

Author: chrisns

.github/workflows/docker-build.yml

@@ -2,6 +2,7 @@
 #
 # Triggers on:
 # - Push to main branch affecting docker/* or drupal/* files
+# - All pull requests (skips build if no relevant files changed)
 # - Manual workflow_dispatch
 #
 # Produces:
@@ -12,12 +13,13 @@ name: Build LocalGov Drupal Container
 
 on:
   push:
-    branches: [main, fix/menu-links-search-index]
+    branches: [main]
     paths:
       - 'cloudformation/scenarios/localgov-drupal/docker/**'
       - 'cloudformation/scenarios/localgov-drupal/drupal/**'
       - 'cloudformation/scenarios/localgov-drupal/.dockerignore'
       - '.github/workflows/docker-build.yml'
+  pull_request:
   workflow_dispatch:
     inputs:
       push_image:
@@ -31,9 +33,32 @@ env:
   IMAGE_NAME: co-cddo/ndx_try_aws_scenarios-localgov_drupal
 
 jobs:
+  changes:
+    name: Check for Docker changes
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+    outputs:
+      docker: ${{ steps.filter.outputs.docker }}
+    steps:
+      - uses: actions/checkout@v6
+      - uses: dorny/paths-filter@v3
+        id: filter
+        with:
+          filters: |
+            docker:
+              - 'cloudformation/scenarios/localgov-drupal/docker/**'
+              - 'cloudformation/scenarios/localgov-drupal/drupal/**'
+              - 'cloudformation/scenarios/localgov-drupal/.dockerignore'
+              - '.github/workflows/docker-build.yml'
+
   build:
     name: Build and Push Container
     runs-on: ubuntu-latest
+    needs: [changes]
+    # Run if: push/dispatch (changes job skipped), OR PR with docker changes
+    if: |
+      always() &&
+      (needs.changes.result == 'skipped' || needs.changes.outputs.docker == 'true')
     permissions:
       contents: read
       packages: write

cloudformation/scenarios/localgov-drupal/docker/Dockerfile

@@ -7,7 +7,7 @@
 # =============================================================================
 # Stage 1: Builder - Install Composer dependencies
 # =============================================================================
-FROM php:8.5-fpm-alpine AS builder
+FROM php:8.3-fpm-alpine AS builder
 
 # Install build dependencies
 RUN apk add --no-cache \
@@ -62,7 +62,7 @@ RUN mkdir -p /var/www/drupal/web/libraries/dropzone \
 # =============================================================================
 # Stage 2: Runtime - Minimal production image
 # =============================================================================
-FROM php:8.5-fpm-alpine AS runtime
+FROM php:8.3-fpm-alpine AS runtime
 
 # Install runtime dependencies
 RUN apk add --no-cache \