Update gitcoverage action to version 4

Author: linkdata

.github/workflows/go.yml

@@ -47,7 +47,7 @@ jobs:
           go tool cover -html=coverage.out -o=coveragereport.html.out
 
       - name: Publish code coverage badge (and optional report)
-        uses: linkdata/gitcoverage@main
+        uses: linkdata/gitcoverage@v4
         with:
           coverage: ${{ steps.coverage.outputs.coverage }}
           report:   "coveragereport.html.out"