accounts/abi/bind/v2: fix error assertion in test

[alarso16]

This part of the WaitDeployedCornerCases test has many issues.

• The real error that should be checked is context.Canceled, which can easily be used.
• The boolean for errors.Is is incorrect, allowing the test to still pass even though the incorrect error is returned.
• The errors are in the wrong order for errors.Is
• err == nil doesn't change the output of this test, since want isn't nil.