mysql should allow tls=preferred option not only skip-verify

[sjones4]

Describe the Bug
The MySQL golang driver supports tls=preferred to use tls when available, else connect without tls:
https://github.com/go-sql-driver/mysql/tree/master#tls

when this parameter is specified in the url an error occurs:

error: open : no such file or directory

there is special handling for tls=skip-verify but not for tls=preferred:
https://github.com/golang-migrate/migrate/blob/v4.16.2/database/mysql/mysql.go#L158

Steps to Reproduce
perform a mysql database migration using the url parameter tls=preferred

Expected Behavior
database migration is successful

Migrate Version
4.16.2

Loaded Source Drivers
any

Loaded Database Drivers
mysql

Go Version
go version go1.21.0 linux/amd64

Stacktrace
N/A

Additional context
This option can be important if mysql is running with --require-secure-transport or non TLS connections are otherwise not permitted.