GH Actions: used a named branch for coverallsapp

The `coverallsapp/github-action` action runner has (finally) created a named branch for the 1.x series, so let's use that.

Ref: coverallsapp/github-action#100

Author: jrfnl

.github/workflows/test.yml

@@ -155,7 +155,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Coveralls Finished
-        uses: coverallsapp/github-action@master
+        uses: coverallsapp/github-action@v1
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           parallel-finished: true