Bump codecov/codecov-action from 5 to 6

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 5 to 6.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v5...v6)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/tests-nightly.yml

@@ -40,6 +40,6 @@ jobs:
           JULIA_DEBUG: PythonCall
           JULIA_NUM_THREADS: '2'
       - uses: julia-actions/julia-processcoverage@v1
-      - uses: codecov/codecov-action@v5
+      - uses: codecov/codecov-action@v6
         with:
           file: lcov.info

.github/workflows/tests.yml

@@ -76,7 +76,7 @@ jobs:
         uses: julia-actions/julia-processcoverage@v1
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
@@ -160,6 +160,6 @@ jobs:
           PYTHON_JULIACALL_PROJECT: ${{ env.MANUAL_TEST_PROJECT }}
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}