Bump wp-cli/wp-cli-tests from 5.1.3 to 5.1.5

Bumps [wp-cli/wp-cli-tests](https://github.com/wp-cli/wp-cli-tests) from 5.1.3 to 5.1.5.
- [Release notes](https://github.com/wp-cli/wp-cli-tests/releases)
- [Commits](wp-cli/wp-cli-tests@v5.1.3...v5.1.5)

---
updated-dependencies:
- dependency-name: wp-cli/wp-cli-tests
  dependency-version: 5.1.5
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]