chore(deps): bump actions/upload-artifact from 5 to 6 (#315)

Bumps [actions/upload-artifact](https://github.com/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
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Andrew Gillis <11790789+gammazero@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/gateway-conformance.yml

@@ -148,13 +148,13 @@ jobs:
         run: cat output.md >> $GITHUB_STEP_SUMMARY
       - name: Upload HTML report
         if: failure() || success()
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: ${{ matrix.backend }}_gateway-conformance.html
           path: output.html
       - name: Upload JSON report
         if: failure() || success()
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: ${{ matrix.backend }}_gateway-conformance.json
           path: output.json