avoid disruption of workflows when coveralls has an API outage (Open-MSS#3012)

Author: ReimarBauer

.github/workflows/testing-all-oses.yml

@@ -33,6 +33,7 @@ jobs:
     - name: Send coverage to Coveralls (parallel)
       uses: coverallsapp/github-action@5cbfd81b66ca5d10c19b062c04de0199c215fb6e # v2.3.7
       with:
+        fail-on-error: false
         debug: true
         parallel: true
         format: cobertura
@@ -46,4 +47,5 @@ jobs:
       - name: Close parallel build
         uses: coverallsapp/github-action@5cbfd81b66ca5d10c19b062c04de0199c215fb6e # v2.3.7
         with:
+          fail-on-error: false
           parallel-finished: true