Update version of Coveralls GitHub Action (#13265)

We had this set to `master` in an attempt to use the rolling release,
except Coveralls added a _new_ branch called `main` that is now the
primary branch, so we had fallen out of date.  One of these effects is
that the action was still attempting to use the deprecating Node 16
runners.

Since we now also have dependabot updating our Actions for us, this
commit sets a fixed release of the Action for better reproducibility.

(cherry picked from commit 18145f9)

.github/workflows/coverage.yml

@@ -71,7 +71,7 @@ jobs:
           lcov --add-tracefile python.info --add-tracefile rust.info --output-file coveralls.info
 
       - name: Coveralls
-        uses: coverallsapp/github-action@master
+        uses: coverallsapp/github-action@v2.3.0
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           path-to-lcov: coveralls.info