Fix: replace shivammathur/setup-php with apt-get install

shivammathur/setup-php is incompatible with Gitea act_runner DinD.
Install PHP + extensions directly via apt-get instead.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/release.yml

@@ -56,11 +56,11 @@ jobs:
           fetch-depth: 0
 
       - name: Setup PHP
-        uses: shivammathur/setup-php@v2
-        with:
-          php-version: '8.1'
-          extensions: mbstring, xml, zip
-          tools: composer:v2
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y -qq php-cli php-mbstring php-xml php-zip php-curl composer >/dev/null 2>&1
+          php -v
+          composer --version
 
       - name: Get version and stability
         id: meta