Fix badges appearance

[janfaracik]

Broken by #9115 - See #9115 (comment).

This PR fixes the badge appearance on light/dark modes.

Before

After

Testing done

• Badges appear as expected in light/dark mode

Proposed changelog entries

• Fix badges appearance

Proposed upgrade guidelines

N/A

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1. The Jira issue, if it exists, is well-described.
2. The changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developers, depending on the change) and are in the imperative mood (see examples). Fill in the Proposed upgrade guidelines section only if there are breaking changes or changes that may require extra steps from users during upgrade.
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8. For new APIs and extension points, there is a link to at least one consumer.

Desired reviewers

@jenkinsci/sig-ux

Before the changes are marked as ready-for-merge:

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[timja]

LGTM, (checked in chrome and safari, looks fine to me)

[daniel-beck]

What's the semantic difference between the two classes here?

[janfaracik]

The alert modifier class feels misused here as the badge isn't an alert (hence I missed this in the alert changes MR). Meanwhile the colour classes are relatively widely used in Jenkins already and are generic classes to modify colours of an element, button behaves the same way.

[NotMyFault]

/label ready-for-merge

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This PR is now ready for merge. We will merge it after ~24 hours if there is no negative feedback.
Please see the merge process documentation for more information about the merge process.
Thanks!