Run integration test PR checks nightly

[angelapwen]

Scheduled for 5AM UTC. This will assist in catching bugs introduced with new runner images.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Confirm the readme has been updated if necessary.
• Confirm the changelog has been updated if necessary.

[aeisenberg]

Oops. Still in draft. Code looks good. Let's if everything passes.

[angelapwen]

Oops. Still in draft. Code looks good. Let's if everything passes.

I still haven't configured a notification to our team if any of these fail (see backlinked issue). I can do that in a follow-up if we want to start running immediately though.

[angelapwen]

Huh... workflow files don't seem to be working with an error message:

Invalid type for `on`

I'll look into it but nothing comes top of mind as schedule is supported (and we use it elsewhere!)

EDIT: I think I see the syntax error, will fix

[angelapwen]

PR check failures are now due to upstream (usually transient) setup-swift failures.

[aeisenberg]

Looks reasonable. If the failures are transient, I'll leave it up to you if you want to override the failures and merge or re-run later.

[angelapwen]

I don't think we have a way to force green on this repo, and I'd rather not make all those checks non-required (and then make them required again later), so I'll wait to re-run.