micro-ROS agent stops on logger setup line

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- Hardware description: micro-ros node: STM32L4 Discovery kit IoT node (B-L475E-IOT01A2), agent: Raspberry Pi 4 Model B 2GB RAM
- RTOS: Zephyr
- Installation type: micro_ros_setup
- Version or commit hash: humble

#### Steps to reproduce the issue

1. Configure firmware to use ping-pong demo application and usb-serial transport.
2. Build and flash.
3. Plug microcontroller into Raspberry and run micro-ros agent.

#### Expected behavior
Micro-ros node starts properly and its topics are visible from Raspberry.

#### Actual behavior
Micro-ros agent stops on:
```
[1667242557.691466] info | TermiosAgentLinux.cpp | init | running... | fd: 3
[1667242557.692280] info | Root.cpp | set_verbose_level | logger setup | verbose_level: 4
```

#### Additional information
I tried to unplug, then plug in the board and resetting it with dedicated pushbutton.
Raspberry runs ROS2 Humble on Ubuntu 22.04 server with kernel:
`Linux ubuntu 5.15.39-rt42-raspi #1 SMP PREEMPT_RT Sat Jul 16 08:34:58 UTC 2022 aarch64 aarch64 aarch64 GNU/Linux`

No source file or test is named. Start by reproducing the issue with the STM32L4 Discovery kit, Zephyr, USB-serial transport, and the micro-ROS agent on the Raspberry Pi, then inspect the agent startup path around the reported logger setup output. Done means the agent stays running and the node's topics are visible from Raspberry Pi.

Written by the indexing model from the issue text.