Bump codecov/codecov-action from 5 to 6 (#589)

Author: dependabot[bot]

.github/workflows/CI.yml

@@ -44,7 +44,7 @@ jobs:
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
       - uses: julia-actions/julia-processcoverage@v1
-      - uses: codecov/codecov-action@v5
+      - uses: codecov/codecov-action@v6
         if: matrix.version == '1'
         with:
           files: lcov.info