[dependabot]: Bump actions/cache from 5 to 6 in the actions group (#422)

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: mne[bot] <50266005+mne-bot@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/tests.yml

@@ -78,7 +78,7 @@ jobs:
           fi
       - run: ./tools/get_testing_version.sh
         working-directory: ../mne-python
-      - uses: actions/cache@v5
+      - uses: actions/cache@v6
         with:
           key: ${{ env.TESTING_VERSION }}
           path: ~/mne_data
@@ -170,7 +170,7 @@ jobs:
           python -m pip install -ve .${PIP_OPTION} ${QT_LIB_INSTALL}
       - run: bash ./tools/get_testing_version.sh
         working-directory: ../mne-python
-      - uses: actions/cache@v5
+      - uses: actions/cache@v6
         with:
           key: ${{ env.TESTING_VERSION }}
           path: ~/mne_data