Make asyncio usage compatible with Python 3.10 (remove deprecation warning)

[lars-petter-hauge]

The get_event_loop method is deprecated in Python 3.10 (https://docs.python.org/3/library/asyncio-eventloop.html#asyncio.get_event_loop). Refactor our usage of asyncio in ert to be compatible with future releases of asyncio

[berland]

Deprecation plan has been changed, this is deprecated from Python 3.12.

The call is currently only being used in https://github.com/equinor/ert/blob/01c1f9a9ffcbe663e2e9c79052ba4ff18e74562e/src/ert/async_utils.py#L20C1-L25C40

[berland]

The RunTimeError caught in this code is triggered by everest's pytest. Erts own tests will pass without the try clause in async_utils.py.

[berland]

The RunTimeError caught in this code is triggered by everest's pytest. Erts own tests will pass without the try clause in async_utils.py.

Not perfectly true, Ert's tests on its everest interface (batch simulation) will fail.

[berland]

Everest gui tested manually to work fine with this.