chore: Update dependency karma to v6.3.15

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
karma (source)	6.3.13 -> 6.3.15

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Release Notes

karma-runner/karma

v6.3.15

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Bug Fixes

• helper: make mkdirIfNotExists helper resilient to concurrent calls (d9dade2), closes /github.com/karma-runner/karma-coverage/issues/434#issuecomment-1017939333

v6.3.14

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Bug Fixes

• remove string template from client code (91d5acd)
• warn when singleRun and autoWatch are false (69cfc76)
• security: remove XSS vulnerability in returnUrl query param (839578c)

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