ci: GHA: codecov: fail_ci_if_error=true

This should make it obvious if missing coverage is due to the upload
having failed.

Using #6553 would be an
alternative, but this can be used already if that takes longer.

Ref: #6463 (comment)

Author: blueyed

.github/workflows/main.yml

@@ -167,7 +167,7 @@ jobs:
         token: ${{ secrets.codecov }}
         file: ./coverage.xml
         flags: GHA
-        fail_ci_if_error: false
+        fail_ci_if_error: true
         name: ${{ matrix.name }}
 
   deploy: