fix: Pinning pytest-asyncio to 0.21.1

[Gmerold]

Description

Pins the version of pytest-asyncio to 0.21.1.
Context: Latest version of pytest-asyncio removes asyncio_event_loop. This makes integration tests hang forever.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have bumped the version of the library