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>
This ensures that while having git remotes to point to either
`github.com` or authenticated GHE instances, adding another git remote
pointing to an unrelated host won't change the remote resolution in any
way, even if the unrelated remote is called `upstream` or `github` (and
thus normally took precedence).
