The `deploy-to-firebase.js` tests rely on git info retrieved from the
`angular/angular` repository (via `git ls-remote ...`).
Previously, different calls to `git ls-remote ...` could return
different values if a new commit was pushed or a new branch was created
during test execution, resulting in errors ([example CI failure][1]).
This commit makes the tests more stable by memoizing the result of
`git ls-remote ...` and returning the same result for subsequent calls
with the same arguments (even if meanwhile the remote has been updated).
[1]: https://circleci.com/gh/angular/angular/877626
PR Close#40088
c18a9d5c79