DockerRegistryConfigAuthentication uses the wrong serverUrl as a fallback for the Credentials helper

[nosan]

Before this commit, the credential helper used the serverUrl from the Map.Entry<String,Auth> as a fallback. However, the helper only uses the email from the auths.

https://github.com/docker/cli/blob/b24e7f85a488da13dc2d5be87acdaab2652634bb/cli/config/credentials/native_store.go#L42-L56

func (c *nativeStore) Get(serverAddress string) (types.AuthConfig, error) {
	// load user email if it exist or an empty auth config.
	auth, _ := c.fileStore.Get(serverAddress)
	creds, err := c.getCredentialsFromStore(serverAddress)
	if err != nil {
		return auth, err
	}
	auth.Username = creds.Username
	auth.IdentityToken = creds.IdentityToken
	auth.Password = creds.Password
	auth.ServerAddress = creds.ServerAddress
	return auth, nil
}