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/main_test_itensors_base_macos_windows.yml

@@ -34,6 +34,6 @@ jobs:
           Pkg.develop(path="./NDTensors");
           Pkg.develop(path=".");
           Pkg.test("ITensors"; coverage=true, test_args=["base"]);
-      - uses: "codecov/codecov-action@v5"
+      - uses: "codecov/codecov-action@v6"
         with:
           token: "${{ secrets.CODECOV_TOKEN }}"

.github/workflows/test_itensors_base_ubuntu.yml

@@ -38,6 +38,6 @@ jobs:
           Pkg.develop(path=".");
           Pkg.test("ITensors"; coverage=true, test_args=["base"]);
           
-      - uses: "codecov/codecov-action@v5"
+      - uses: "codecov/codecov-action@v6"
         with:
           token: "${{ secrets.CODECOV_TOKEN }}"