Timeout in pruning job

Getting logs like
```
2022-02-15 09:19:54,828 - root - INFO - Done downloading corpus. Contains 5964 elements.
Traceback (most recent call last):
File "/opt/oss-fuzz/infra/cifuzz/cifuzz_combined_entrypoint.py", line 40, in
sys.exit(main())
File "/opt/oss-fuzz/infra/cifuzz/cifuzz_combined_entrypoint.py", line 36, in main
return run_fuzzers_entrypoint.run_fuzzers_entrypoint()
File "/opt/oss-fuzz/infra/cifuzz/run_fuzzers_entrypoint.py", line 61, in run_fuzzers_entrypoint
result = run_fuzzers.run_fuzzers(config)
File "/opt/oss-fuzz/infra/cifuzz/run_fuzzers.py", line 302, in run_fuzzers
if not fuzz_target_runner.run_fuzz_targets():
File "/opt/oss-fuzz/infra/cifuzz/run_fuzzers.py", line 130, in run_fuzz_targets
result = self.run_fuzz_target(target)
File "/opt/oss-fuzz/infra/cifuzz/run_fuzzers.py", line 161, in run_fuzz_target
result = fuzz_target_obj.prune()
File "/opt/oss-fuzz/infra/cifuzz/fuzz_target.py", line 140, in prune
result = engine_impl.minimize_corpus(self.target_path, [],
File "/usr/local/lib/python3.8/dist-packages/clusterfuzz/_internal/bot/fuzzers/libFuzzer/engine.py", line 507, in minimize_corpus
raise TimeoutError('Merging new testcases timed out\n' + result.output)
TimeoutError: Merging new testcases timed out
INFO: Running with entropic power schedule (0xFF, 100).
```

Increasing `FUZZ_SECONDS` does not seem to be enough to fix this...
But I see `fuzz_seconds // fuzzers_left_to_run` so maybe this fuzzer is a bit long but it should have more time than the others...