git-try-push: fix truth-y string arguments

[carlocab]

When we pass false to force and no_lease, it is cast as a String. Unfortunately, the string 'false' is truth-y, so we've been pushing with --force since we started using these inputs.

Let's fix that by making sure we interpret string arguments as intended.

[carlocab]

Working as intended: https://github.com/Homebrew/homebrew-core/actions/runs/4584208201/jobs/8095556400#step:10:29

[MikeMcQuaid]

Thanks @carlocab!