ci: fix coverage upload

At least on my local system, there's no suffix.

Author: gadomski

.github/workflows/tests.yml

@@ -1,8 +1,10 @@
 name: Tests
 
 on:
-  - push
-  - pull_request
+  push:
+    branches:
+      - main
+  pull_request:
 
 jobs:
   tests:
@@ -96,6 +98,8 @@ jobs:
         with:
           name: coverage-data
           path: ".coverage.*"
+          if-no-files-found: error
+          include-hidden-files: true
 
       - name: Upload documentation
         if: matrix.session == 'docs-build'