Bump actions/upload-artifact from 5 to 6 in the actions group

Bumps the actions group with 1 update: [actions/upload-artifact](https://github.com/actions/upload-artifact).


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

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

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

Author: dependabot[bot]

.github/workflows/continuous-integration.yml

@@ -181,7 +181,7 @@ jobs:
           zip -r simple-wp-optimizer.zip simple-wp-optimizer
           
       - name: Upload build artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: simple-wp-optimizer
           path: build/simple-wp-optimizer.zip