froze ubuntu version

Author: michalsn

Diff for: .github/workflows/phpunit.yml

@@ -34,7 +34,7 @@ env:
 jobs:
   main:
     name: PHP ${{ matrix.php-versions }} - ${{ matrix.db-platforms }}
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
     strategy:
       matrix: