Describe the Bug
MySQL database driver reads a CA certificate file from the path specified by x-tls-ca parameter, if tis parameter in the DSN is not true, false, or skip-verify. This helps establishing TLS connections to the database with the CA file. However, when the TLS configuration is already registered using mysql.RegisterTLSConfig, the driver overrides it, reading x-tls-ca parameter even if the file does not exist (and occurs an error).

Steps to Reproduce

1. Register a tls.Config using mysql.RegisterTLSConfig
2. Use migrate.New with the registered TLS configuration name (e.g. ...?tls=aws)
3. An error occurs: open : no such file or directory

Expected Behavior
I think MySQL driver of migrate should ignore registering TLS config from the DSN if x-tls-ca is not provided. Checking the configuration is already registered is a better solution, but go-mysql-driver does not provide a method to check the configuration name is known or not.

Migrate Version
v4.16.2

Loaded Source Drivers
file

Loaded Database Drivers
mysql, stub

Go Version
go version go1.20.7 darwin/arm64

Stacktrace
N/A

Additional context
N/A