Bump wp-cli/extension-command from 2.1.5 to 2.1.6

Bumps [wp-cli/extension-command](https://github.com/wp-cli/extension-command) from 2.1.5 to 2.1.6.
- [Release notes](https://github.com/wp-cli/extension-command/releases)
- [Commits](wp-cli/extension-command@v2.1.5...v2.1.6)

---
updated-dependencies:
- dependency-name: wp-cli/extension-command
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]