Fix missing CSS namespace on active IDE tab class

[rezrah]

Summary

🧹 Tidying up

Contributor checklist:

• All new and existing CI checks pass
• Tests prove that the feature works and covers both happy and unhappy paths
• Any drop in coverage, breaking changes or regressions have been documented above
• UI Changes contain new visual snapshots (generated by adding update snapshots label to the PR)
• All developer debugging and non-functional logging has been removed
• Related issues have been referenced in the PR description

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[changeset-bot]

🦋 Changeset detected

Latest commit: 27de2dd

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 7 packages

Name	Type
@primer/react-brand	Patch
@primer/brand-docs	Patch
@primer/brand-primitives	Patch
@primer/brand-e2e	Patch
@primer/brand-fonts	Patch
@primer/brand-config	Patch
@primer/brand-storybook	Patch

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[github-actions]

🟢 No design token changes found

[github-actions]

⚠️ Visual differences found

Our visual comparison tests found UI differences.

Please review the differences by using the test artifacts to ensure that the changes were intentional.

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If the changes are expected, please run npm run test:visual:update-snapshots to replace the previous fixtures.

Review visual differences

[joshfarrant]

Good spot, thanks!