Jobs such as https://gitlab.com/gitlab-org/gitlab-foss/-/jobs/1686583500
were intermittently failing because the Authorization header would have
slightly different JWTs. It turns out the `iat` and `exp` fields were
off by a second since the test might generate the field before the test
made the HTTP request.

We fix this issue by freezing the time whenever we need to make an HTTP
request.