Enable pg_stat_statements in PostgreSQL containers

This change modifies the GitHub Actions workflow to enable the `pg_stat_statements` extension in PostgreSQL service containers during tests. It ensures the required settings are applied and the database is properly restarted to reflect the changes, improving compatibility checks and diagnostics.

.github/workflows/pg-compat-matrix.yml

@@ -41,6 +41,28 @@ jobs:
       - name: Install backend dependencies
         run: pip install -r backend/requirements.txt
 
+      - name: Enable pg_stat_statements in service container
+        run: |
+          PG_CID="$(docker ps --filter "ancestor=postgres:${{ matrix.pg_version }}" --format "{{.ID}}" | head -n1)"
+          if [ -z "$PG_CID" ]; then
+            echo "Could not find postgres service container for version ${{ matrix.pg_version }}"
+            docker ps -a
+            exit 1
+          fi
+
+          echo "Using postgres container: $PG_CID"
+          docker exec "$PG_CID" psql -U postgres -d compatdb -c "ALTER SYSTEM SET shared_preload_libraries = 'pg_stat_statements';"
+          docker restart "$PG_CID"
+
+          for i in $(seq 1 40); do
+            if docker exec "$PG_CID" pg_isready -U postgres -d compatdb; then
+              break
+            fi
+            sleep 2
+          done
+
+          docker exec "$PG_CID" psql -U postgres -d compatdb -c "CREATE EXTENSION IF NOT EXISTS pg_stat_statements;"
+
       - name: Run PostgreSQL compatibility smoke checks
         env:
           PG_DSN_CANDIDATES: postgresql://postgres:postgres@postgres:5432/compatdb?sslmode=disable,postgresql://postgres:postgres@127.0.0.1:5432/compatdb?sslmode=disable