Set timezone for karma CI job to Etc/UTC (UTC+0)

What does this MR do?

Forces Etc/UTC (aka UTC+0 or UTC) as timezone for the karma CI job when the job was executed in both developer's local and CI environments.

Are there points in the code the reviewer needs to double check?

No. 'Europe/London' was selected due to 'en-*' locale and UTC-6/UTC+5 timezone. Note that we can't choose any other timezone outside of UTC-6 and UTC+5 such as 'America/Los_Angeles' or 'Asia/Tokyo'.

Finally I decided to use Etc/UTC.

Why was this MR needed?

Because karma CI job fails in env between UTC-7 and UTC-12 or between UTC+6 and UTC+12. It is considered that GitLab CI could not detect this problem as it was run on the UTC+0 environment.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [n/a] Documentation created/updated
• [n/a] API support added
• [n/a] Tests added for this feature/bug
• Review
  • [n/a] Has been reviewed by UX
  • [n/a] Has been reviewed by Frontend
  • Has been reviewed by Backend
  • [n/a] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• [n/a] Internationalization required/considered

What are the relevant issue numbers?

Closes #42251 (closed)