build(deps): bump actions/upload-artifact from 5 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v5...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/redis.yml

@@ -75,7 +75,7 @@ jobs:
           echo "DIGEST_NAME=$(echo ${{ matrix.platform }} | sed 's,/,-,g')" >> $GITHUB_OUTPUT
       - name: Upload digest
         if: ${{ github.event_name != 'pull_request' }}
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: digest-${{ steps.digest.outputs.DIGEST_NAME }}
           path: /tmp/digests/*

.github/workflows/reusable-kumomta-build.yml

@@ -102,7 +102,7 @@ jobs:
         ./assets/sign-rpm.sh *.rpm
 
     - name: "Upload artifact"
-      uses: actions/upload-artifact@v5
+      uses: actions/upload-artifact@v6
       with:
         name: "${{ inputs.artifact_name }}"
         path: |
@@ -227,7 +227,7 @@ jobs:
           touch "${{ runner.temp }}/digests/${digest#sha256:}"
 
       - name: Upload digest
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: digests-${{ inputs.artifact_name }}
           path: ${{ runner.temp }}/digests/*