Bump vega from 5.22.0 to 5.26.1 in /ui-tests

Bumps [vega](https://github.com/vega/vega) from 5.22.0 to 5.26.1.
- [Release notes](https://github.com/vega/vega/releases)
- [Commits](vega/vega@v5.22.0...v5.26.1)

---
updated-dependencies:
- dependency-name: vega
  dependency-type: indirect
...

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