Allow windows to continue on cache restore error

[jamesmunns]

Mitigation for #2535

[jamesmunns]

One tricky thing about this approach is that I don't know how we'd be able to determine if this mitigation is REALLY working or not (as the issue is intermittent!), short of looking at "builds that took a bit longer" in the actions history.

We'll definitely know if it doesn't work, as we'll still see CI failures on Windows.

[hawkw]

Personally, I think this is better than not having it, even though I agree that it's gonna be kinda hard to tell if it's working..

[emilyalbini]

Before merging this I'd rather enable debug logging in all workflows. If we merge this too it's going to be harder to notice when it fails (and when to grab the logs).

[jamesmunns]

Converting to draft so we remember that we might not want to merge this until we've had time to debug this. See #2540 for context.