Bump karma from 6.3.12 to 6.3.15

Bumps [karma](https://github.com/karma-runner/karma) from 6.3.12 to 6.3.15.
- [Release notes](https://github.com/karma-runner/karma/releases)
- [Changelog](https://github.com/karma-runner/karma/blob/master/CHANGELOG.md)
- [Commits](https://github.com/karma-runner/karma/compare/v6.3.12...v6.3.15

)

---
updated-dependencies:
- dependency-name: karma
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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