Bump actions/upload-artifact from 3 to 4

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 3 to 4.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v3...v4)

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

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/gateway-conformance.yml

@@ -100,13 +100,13 @@ jobs:
         run: cat output.md >> $GITHUB_STEP_SUMMARY
       - name: Upload HTML report
         if: failure() || success()
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: gateway-conformance.html
           path: output.html
       - name: Upload JSON report
         if: failure() || success()
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: gateway-conformance.json
           path: output.json