Bump actions/upload-artifact from 4 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v4...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/docker_build.yml

@@ -98,7 +98,7 @@ jobs:
       -
         name: Upload digest
         if: github.event_name != 'pull_request'
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: digests-${{ matrix.platform-slug }}
           path: /tmp/digests/*

.github/workflows/docker_frankenphp.yml

@@ -99,7 +99,7 @@ jobs:
       -
         name: Upload digest
         if: github.event_name != 'pull_request'
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: digests-${{ matrix.platform-slug }}
           path: /tmp/digests/*