Re-evaluate caching_sha2_password addition on PHP < 7.4

[swissspidy]

In #220, we replaced mysql_native_password with caching_sha2_password.

That seemed to work fine everywhere, but in the wp-cli-bundle repo there are some warnings:

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

Nowhere else though 🤔

Maybe we need to update the tests script to change that conditionally based on the PHP version.

[swissspidy]

Maybe it has more to do with the setup on that repo though? Will add details at wp-cli/wp-cli-bundle#666