Change default branch label colors for dark theme

[gtsiolis]

Description

This will add color support for dark theme for the default branch label, following the label specs used in #4607.

BEFORE	AFTER

How to test

1. Enable Teams & Projects by going to /new.
2. Add a project using GitLab provider since GitHub integration is not ready to use in preview environments.
3. Once you add a project, go to Branches for that project. Make sure there's a default branch with at least one commit.

Release Notes

Change default branch label colors for dark theme

[gtsiolis]

Hey @AlexTugarev! Could you take a look at this minor change since you initially added this label in #4970? 🏀

[AlexTugarev]

/werft run

👍 started the job as gitpod-build-gt-change-default-branch-label-colors.1

[AlexTugarev]

Change looks good! 🙏🏻

/lgtm
/approve no-issue

[roboquat]

LGTM label has been added.

Git tree hash: 2c256796ef180f89ed4ce4fb35f5cbc11f1f000d

[AlexTugarev]

/approve no-issue

[roboquat]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AlexTugarev

Associated issue requirement bypassed by: AlexTugarev

The full list of commands accepted by this bot can be found here.

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• components/dashboard/OWNERS [AlexTugarev]

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[gtsiolis]

Danke @AlexTugarev! 🏓