Exit with a status of 1 if any test fails

[tinywombat765]

As promised. Not sure if you want these changes but here they are if you do.

[michael-lazar]

I actually snuck this in https://github.com/michael-lazar/gemini-diagnostics/commit/e7704294b13f455b368b29759fe33e6ace2543b1 a few days before you made this PR 😄