mssql named instance port number

Describe the bug
When connecting to an mssql named instance, the connection string generated in tortoise.mssql.client.MSSQLClient still includes the port number. Named instances listen on dynamic ports, so the ,{port} should be left out, otherwise it tries to connect by default to port 1433 which fails.

To Reproduce
Create an mssql connection with host containing a named instance, for example my_server\my_instance

Expected behavior
It should work

Additional context
One possible fix could be:

    if "\\" in host:
        # named instance, don't provide port
        server = host
    else:
        server = f"{host},{port}"
    self.dsn = f"DRIVER={driver};SERVER={server};UID={user};PWD={password};"

Start in tortoise.mssql.client.MSSQLClient and inspect how the connection string builds its SERVER value from the host and port. Reproduce the named-instance case with a host such as my_server\my_instance, then verify that named instances omit the port while ordinary hosts retain it and connections still work.