CredentialsCannotBeLinkedException
Thrown when attempting to link credentials that are not supported.
Reasons for this can e.g. be:
Linking an email account with an anonymous account. Only the other direction is supported, i.e.
anonymousUser.linkCredentials(Credentials.emailPassword(email, password))
Linking two email accounts.
Linking an account with itself.
The exact reason is found in the exception message.