Merge pull request #1508 from Bastian-Krause/bst/codecov-bump

update codecov/codecov-action v3 -> v4

Author: Bastian-Krause

.github/workflows/reusable-unit-tests.yml

@@ -67,4 +67,4 @@ jobs:
         # check README.rst separately
         pip install rstcheck
         rstcheck --ignore-languages=bash --report-level=WARNING README.rst
-    - uses: codecov/codecov-action@v3
+    - uses: codecov/codecov-action@v4