For the "cli" and "tui" modes of the test runner there's a "-race" parameter to
turn it on; for running tests on CI with go test, you turn it on by setting the
environment variable LAZYGIT_RACE_DETECTOR to a non-empty value.
This is useful for example to pass both -slow and -debug. Since we're about to
add yet another flag in the next commit, it becomes even more important. Plus,
it makes the code a little nicer too.
