ci: update coverallsapp/github-action from master to v2 (#1071)

Pin the Coveralls action to a stable versioned tag instead of master
to avoid unintended breaking changes from upstream.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: thomaspoignant

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
       - run: npm run test
       - run: mkdir ./coverage && npm run coverage > ./coverage/lcov.info
       - name: Coveralls
-        uses: coverallsapp/github-action@master
+        uses: coverallsapp/github-action@v2
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}