Use ubuntu-22.04 runner instead of buildjet for the UI tests

[jmartinesp]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

• Remove the BuildJet runner from our CI jobs.
• Make the UI test one run only after merging PRs or manually for a branch, since it's not really maintained.

Motivation and context

We want to get rid of the BuildJet runners.

Checklist

• Changes has been tested on an Android device or Android emulator with API 21
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/element-hq/element-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request includes a new file under ./changelog.d. See https://github.com/element-hq/element-android/blob/develop/CONTRIBUTING.md#changelog
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR
• If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()

[bmarty]

Thanks, just one question

[bmarty]

Why not using ubuntu-latest?

[jmartinesp]

We've used -latest in the past and sometimes that led to unintended dependency upgrades of the software included in the runners, so I thought it would be better to keep the same version.

[bmarty]

Same remark