ci(deps): 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](actions/upload-artifact@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] <[email protected]>

Author: dependabot[bot]

.github/workflows/deploy.yml

@@ -118,7 +118,7 @@ jobs:
           echo "✅ All critical assets verified successfully"
 
       - name: Upload build artifacts
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: site-build
           path: _site/

.github/workflows/manual-deploy.yml

@@ -58,7 +58,7 @@ jobs:
           JEKYLL_ENV: production
 
       - name: Upload artifacts
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: site-${{ inputs.environment }}-${{ github.sha }}
           path: _site/

.github/workflows/test-multilingual.yml

@@ -51,7 +51,7 @@ jobs:
         ./test-multilingual.sh
     
     - name: Upload build artifacts on failure
-      uses: actions/upload-artifact@v4
+      uses: actions/upload-artifact@v6
       if: failure()
       with:
         name: build-artifacts