Increase timeout for tests generating Semaphore proofs

[vplasencia]

Description

There is an error when running the test workflow:

Proof › # generateProof › Should generate a Semaphore proof

    thrown: "Exceeded timeout of 20000 ms for a test.

https://github.com/semaphore-protocol/semaphore/actions/runs/8894821856/job/24423871569

[sripwoud]

There are 2 different issues in that test(s):

• Timeout for the proof generation:
  Increasing timeout can probably fix it. But I think the root cause is related to Error in the production and pull-requests workflows privacy-scaling-explorations/zk-kit#280 (comment)
• Structure of the test:
  Here
  We use a proof defined in the outer scope as parameter. It makes the tests depend on each others. As a result the test suite may produce unexpected results: a successful proof verification test requires the proof generation test having completed first, but jest executes everything in parallel...