fix(mysql): percent-decode database name

[abonander]

Duplicates the fix to Postgres in #3593 to the MySQL driver.

The SQLite driver already does this:

sqlx/sqlx-sqlite/src/options/parse.rs

Lines 29 to 32 in e3ef8ba

	&*percent_decode_str(database)
	.decode_utf8()
	.map_err(Error::config)?,
	)