Suppress terminal logging in CI tests

[albertvillanova]

Suppress terminal logging in CI tests.

The approached I followed: I set logger.level = -1 for CI tests.

Fix #503.

Agent tests:

• Before:

tests/test_agents.py::TestMultiStepAgent::test_logging_to_terminal_is_disabled FAILED
tests/test_agents.py::TestMultiStepAgent::test_step_number ╭────────────────────────────────── New run ───────────────────────────────────╮
│                                                                              │
│ Test task                                                                    │
│                                                                              │
╰─ MagicMock - <MagicMock name='mock.model_id' id='140456269450064'> ──────────╯
PASSED
tests/test_agents.py::TestMultiStepAgent::test_planning_step_first_step ───────────────────────────────── Initial plan ─────────────────────────────────
Here is the plan of action that I will follow to solve the task:
```
<MagicMock name='mock().content' id='140456269040704'>
```
PASSED

• With this PR:

tests/test_agents.py::TestMultiStepAgent::test_logging_to_terminal_is_disabled PASSED
tests/test_agents.py::TestMultiStepAgent::test_step_number PASSED
tests/test_agents.py::TestMultiStepAgent::test_planning_step_first_step PASSED

[aymeric-roucher]

Great change, thanks @albertvillanova !