Escape theme test locator regexp

[ErisDS]

Summary

• Escapes theme names before constructing the installed-theme Playwright locator regexp.
• Follows up on CodeRabbit nitpick from ✨ Added a built-in theme code editor #27656 so future fixture names with regexp metacharacters match literally.

Testing

• pnpm --filter @tryghost/admin-x-settings exec eslint --cache test/acceptance/site/theme.test.ts

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 9f59480 and 91b4cb6.

📒 Files selected for processing (1)

• apps/admin-x-settings/test/acceptance/site/theme.test.ts

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Walkthrough

This PR adds a local escapeRegExp helper function to the theme test file and applies it to safely filter theme list items by name. The change prevents regex metacharacters (such as *, +, ., ?, and others) from being interpreted as regex syntax when constructing the theme name filter. The installed-theme editor UI lookup now escapes the theme name before building a case-insensitive RegExp for comparison, ensuring theme names with special characters are matched literally.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: escaping the theme test locator regexp to prevent regex metacharacters from causing unintended behavior.
Description check	✅ Passed	The description is directly related to the changeset, explaining the purpose of escaping theme names in the test locator and referencing the previous PR context.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/escape-theme-test-regexp

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