[5.x] Use ubuntu-latest in GitHub Actions workflows (#11443)

Author: duncanmcclean

.github/workflows/release.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout code
         uses: actions/checkout@v4

.github/workflows/tests.yml

@@ -103,7 +103,7 @@ jobs:
         run: vendor/bin/phpunit
 
   js-tests:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 
     name: JavaScript tests