Fix libmysql download to stable URL

[skip ci] Backport libmysql build fix (d9a9696)

[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