[CI] Integration failure: staging instance

[github-actions]

Staging instance failure

A scheduled test against Sigstore's staging instance has failed.

This suggests one of three conditions:

• A backwards-incompatible change in a Sigstore component;
• A regression in sigstore-python;
• A transient error.

The full CI failure can be found here:

https://github.com/sigstore/sigstore-python/actions/runs/5190774391

[woodruffw]

This looks like a regression with #645 -- we might be too strict about the claims we expect in ambient tokens.

@di: looks like you were right about this exception needing to be better 🙂

[di]

@di: looks like you were right about this exception needing to be better 🙂

Ah, yep. Let's make sure this gets fixed before the next release.