[skip ci] Don't generate junit.xml in libmysqlclient for now

We're not uploading it anyway, and it makes the verify generated files
step fail.

[skip ci] Fix libmysqlclient build for >=PHP-8.2

Inputs are implicitly coerced to strings...

[skip ci] Attempt to fix libmysqlclient build for >=PHP-8.2

Migrate libmysqlclient job to GitHub actions

Closes GH-9608