Incorrect log message for usage with domain names

[jackwotherspoon]

There is buggy logic around a Dial log message:

cloud-sql-go-connector/dialer.go

Lines 348 to 350 in fef405b

	// Log if resolver changed the instance name input string.
	if cn.String() != icn {
	d.logger.Debugf(ctx, "resolved instance %s to %s", icn, cn)

When Dial is called with a DNS domain name as the icn this logic message code path will always be executed (even if the domain name still points at the same instance) even when it shouldn't be.

The reason being that cn.String() has additional formatting done to it:

cloud-sql-go-connector/instance/conn_name.go

Lines 41 to 44 in fef405b

	func (c *ConnName) String() string {
	if c.domainName != "" {
	return fmt.Sprintf("%s -> %s:%s:%s", c.domainName, c.project, c.region, c.name)
	}

Example: If a user calls Dial with the domain name example.com as the icn.
Then cn.String() would always return example.com -> my-project:region:instance
and continuously log a debug message.

[hessjcg]

This is a good starter issue.