Deployment failing because of caching_sha2_password change

[swissspidy]

In wp-cli/wp-cli-tests#220, we replaced mysql_native_password with caching_sha2_password.

That seemed to work fine everywhere, but there are warnings & thus failures in the deployment step.

See https://github.com/wp-cli/wp-cli-bundle/actions/runs/11257982684/job/31305127211#step:15:218 and wp-cli/wp-cli-tests#226

[swissspidy]

On difference here is that we're using the default provided MySQL server rather than shogo82148/actions-setup-mysql (where we set default_authentication_plugin=mysql_native_password too)