remove Wandalen/wretry.action, call pnpm install directly

The wretry action isn't node24-compatible, so it blocks upgrading
workflow actions to node24. Replace it with plain pnpm install steps.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/nightly-update-source-languages.yaml

@@ -26,11 +26,7 @@ jobs:
           node-version-file: package.json
           cache: pnpm
       - name: pnpm install
-        uses: Wandalen/wretry.action@master
-        with:
-          command: pnpm install --frozen-lockfile
-          attempt_limit: 3
-          attempt_delay: 2000
+        run: pnpm install --frozen-lockfile
       - name: Extract language strings
         run: pnpm intl:extract
       - name: Create commit