Figure out why repo secrets aren't available to CI workflow

[humphd]

In #111 I've added integration tests, which require access to repo secrets for Stripe API keys. I had hoped that landing this on main would make them available, but clearly there's more to the problem, since it still doesn't work, see: https://github.com/mekkim/donatemask/runs/6533686779?check_suite_focus=true

I'll iterate on this next week and figure out what's happening. Until then, please don't rebase prod onto main; or if we need to do that, I'll back this out first.

[humphd]

I've got it working on my fork's main branch, so this is possible, see https://github.com/humphd/donatemask/actions/runs/2372367518. Just need to figure out why it doesn't work here.

[humphd]

This is fixed!