This commit replaces `os.Setenv` with `t.Setenv` in tests. The
environment variable is automatically restored to its original value
when the test and all its subtests complete.
Reference: https://pkg.go.dev/testing#T.Setenv
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>
If these tests are going to exerise `factory.New()`, the config getter
should always be overriden since the default config getter reads from
`~/.config/gh` and thus makes tests dependent on the user's environment.
