Update wp-cli/wp-cli-tests requirement from ^3 to ^4

[dependabot[bot]]

Updates the requirements on wp-cli/wp-cli-tests to permit the latest version.

Release notes

Sourced from wp-cli/wp-cli-tests's releases.

Version 4.0.0

• Use host when checking MySQL server [#173]
• Update to WPCS v3 [#176]

Commits

• bd3f6d6 Update to WPCS v3 (#176)
• 1d25e64 Merge pull request #173 from atoomic/tests-mysql-host
• 145cfba Use host when checking MySQL server
• 58ef38d Merge pull request #171 from wp-cli/fix/use-http-request-helper
• 4bacfe2 Use http_request() helper instead of Requests directly
• 6d0ee4f Update file(s) from wp-cli/.github
• b8d4272 Update FeatureContext::$result and FeatureContext::$email_sends property ...
• 92361ff Update FeatureContext::$result and FeatureContext::$email_sends property ...
• ea27e6e Using TEST_DB where it should be TEST_USER (#169)
• 2e31d19 Use POSIX-compatible counter incrementing (#168)
• Additional commits viewable in compare view

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[swissspidy]

Handled in #80

[dependabot[bot]]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version. You can also ignore all major, minor, or patch releases for a dependency by adding an ignore condition with the desired update_types to your config file.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.