Fix timestamp tests

[ramonpetgrave64]

Client support for Rekor V2: sigstore-python

Summary

Resolves #1405

Fixes the TSA tests that run in CI.

Testing

TSA tests now succeed without error

https://github.com/sigstore/sigstore-python/actions/runs/15173918751/job/42670246342?pr=1406#step:7:1070

============================= test session starts ==============================
platform linux -- Python 3.9.22, pytest-8.3.5, pluggy-1.6.0
rootdir: /home/runner/work/sigstore-python/sigstore-python
configfile: pyproject.toml
plugins: cov-6.1.1
collected 194 items / 187 deselected / 7 selected

2025-05-21T22:37:02.364Z	INFO	restapi/configure_timestamp_server.go:103	[fv-az1372-936/dQUJcpATck-000001] "POST http://localhost:3000/api/v1/timestamp HTTP/1.1" from 127.0.0.1:32890 - 201 1145B in 321.278µs
2025-05-21T22:37:02.378Z	INFO	restapi/configure_timestamp_server.go:103	[fv-az1372-936/dQUJcpATck-000002] "POST http://localhost:3000/api/v1/timestamp HTTP/1.1" from 127.0.0.1:32904 - 201 1144B in 242.6µs
test/unit/internal/test_timestamping.py ....                             [ 57%]
test/unit/test_sign.py sss                                               [100%]

Release Note

• Fixed the Timestamp Authority test data to use the latest signing config format.

Documentation

None

[jku]

lgtm, thanks.

This is not the first time the optional tsa tests are silently failing on CI... would be good to have a better solution here

[jku]

/gcbrun