MQTT - unit test fail before validation checks can run

[rapcmia]

Describe the bug

While checking the MQTT event-name validation work by using this #7977, the existing MQTT unit test path failed before the actual validation logic could be tested. The test file reached shared setup and then failed because it called `MockPaperExchange(client_config_map=...) even though the current constructor no longer accepts that keyword. ❌

Before of this failure, the MQTT test file could not reach the PR specific validation path. This blocks automated verification for MQTT-related changes and makes it harder to tell whether a new MQTT fix is correct without extra test harness work

See attached file for reference

Steps to reproduce

• Conda activate hummingbot
• Run pytest -q test/hummingbot/remote_iface/test_mqtt.py
• Observe that the test file fails during shared setup before the MQTT validation logic is exercised

Attach required files

13052026_test_mqtt.log