fix(gotrue): AuthException .toString method

[TillJohanndeiter]

What kind of change does this PR introduce?

I was a little bit confused by the logs because the AuthException doesn't contain a variable errorCode.

What is the current behavior?

The toString output is not aligned with the variable name

What is the new behavior?

The toString output is aligned with the variable name

Additional context

None

[coveralls]

Pull Request Test Coverage Report for Build 14273398567

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 1 (0.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 75.426%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/gotrue/lib/src/types/auth_exception.dart	0	1	0.0%

Totals
Change from base Build 14080727348:	0.0%
Covered Lines:	2836
Relevant Lines:	3760

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💛 - Coveralls

[dshukertjr]

Thanks for this!