[BUG]: Fix missing return when using `errors.As`

[stevehipwell]

Expected Behavior

When an error is returned from the GitHub API it should result in a provider error unless the behaviour is explicitly expected and coded for.

Actual Behavior

There are code paths in the provider where an error is checked for nil and then only handled if it's a specific type as there is no catch-all return err.

Terraform Version

n/a

Affected Resource(s)

n/a

Terraform Configuration Files

Steps to Reproduce

No response

Debug Output

Panic Output

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