Fix wrapped errors checks

[paskal]

As errors can be wrapped in recent versions of Go, the proper way to check the error types are errors.As and errors.Is.

[github-actions]

Pull Request Test Coverage Report for Build 6476003936

• 2 of 4 (50.0%) changed or added relevant lines in 2 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 84.23%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
backend/app/main.go	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
backend/app/notify/notify.go	2	94.55%

Totals
Change from base Build 6472903539:	-0.01%
Covered Lines:	5811
Relevant Lines:	6899

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💛 - Coveralls