Update dependency @testing-library/react to v12.1.5

Editor assessment

The subject names @testing-library/react and the target version v12.1.5, which fully determines the change at a glance. The chore type and deps scope are accurate for a test-library maintenance bump, and no body is required for a routine version update whose motivation is inherent to dependency upkeep. No footers are present, so there is nothing malformed and nothing noisy to evaluate. Style hygiene is good: imperative phrasing, no trailing period, no ticket junk, moderate subject length, single language. The message communicates everything a reader needs in one line, misleads nowhere, and stands as a tidy, publishable maintenance example.