Fix Python heredoc: use os.environ instead of shell var expansion

Quoted heredoc (<< 'PYEOF') prevents shell expansion of ${VAR}.
Pass values via exported env vars and read with os.environ in Python.

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

templates/workflows/joomla/auto-release.yml.template

@@ -553,15 +553,16 @@ jobs:
             TAR_URL="${GITEA_URL}/${GITEA_ORG}/${GITEA_REPO}/releases/download/${RELEASE_TAG}/${TAR_NAME}"
 
             # Use Python to update only the stable entry's downloads + sha256
+            export PY_ZIP_URL="$ZIP_URL" PY_TAR_URL="$TAR_URL" PY_SHA="$SHA256_ZIP"
             python3 << 'PYEOF'
-          import re
+          import re, os
 
           with open("updates.xml") as f:
               content = f.read()
 
-          zip_url = "${ZIP_URL}"
-          tar_url = "${TAR_URL}"
-          sha = "${SHA256_ZIP}"
+          zip_url = os.environ["PY_ZIP_URL"]
+          tar_url = os.environ["PY_TAR_URL"]
+          sha = os.environ["PY_SHA"]
 
           # Find the stable update block and replace its downloads + sha256
           def replace_stable(m):