Bump guzzlehttp/guzzle from 7.14.2 to 7.15.1

Bumps guzzlehttp/guzzle from 7.14.2 to 7.15.1.

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updated-dependencies:

• dependency-name: guzzlehttp/guzzle
  dependency-version: 7.15.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
  ...

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Fixes 0037286, PR https://github.com/mantisbt/mantisbt/pull/2250