`run_sync` handles `RuntimeError` raised by coroutine incorrectly

[hugokerstens]

Problem

The function jupyter_core.utils.run_sync mistakenly catches a RuntimeError raised by a coroutine and assumes no event loop is running.

If a coroutine handled by run_sync raises a RuntimeError while an event loop is running, it assumes the RuntimeError comes from asyncio.get_running_loop(). This causes calling any coroutine that raises a RuntimeError to raise an error that no event loop is running, since run_sync will attempt to set a new event loop.

How to reproduce

Open a jupyter notebook, or any other context where an event loop is already running. Execute this code:

from jupyter_core.utils import run_sync
async def f():
    raise RuntimeError("My runtime error")

run_sync(f)()

Output

The code raises a RuntimeError: This event loop is already running

Full traceback

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
Cell In[32], line 5
      2 async def f():
      3     raise RuntimeError
----> 5 run_sync(f)()

File [/opt/conda/lib/python3.9/site-packages/jupyter_core/utils/__init__.py:165](http://localhost:8888/opt/conda/lib/python3.9/site-packages/jupyter_core/utils/__init__.py#line=164), in run_sync.<locals>.wrapped(*args, **kwargs)
    163 # Run the loop for this thread.
    164 loop = ensure_event_loop()
--> 165 return loop.run_until_complete(inner)

File [/opt/conda/lib/python3.9/asyncio/base_events.py:623](http://localhost:8888/opt/conda/lib/python3.9/asyncio/base_events.py#line=622), in BaseEventLoop.run_until_complete(self, future)
    612 """Run until the Future is done.
    613 
    614 If the argument is a coroutine, it is wrapped in a Task.
   (...)
    620 Return the Future's result, or raise its exception.
    621 """
    622 self._check_closed()
--> 623 self._check_running()
    625 new_task = not futures.isfuture(future)
    626 future = tasks.ensure_future(future, loop=self)

File [/opt/conda/lib/python3.9/asyncio/base_events.py:583](http://localhost:8888/opt/conda/lib/python3.9/asyncio/base_events.py#line=582), in BaseEventLoop._check_running(self)
    581 def _check_running(self):
    582     if self.is_running():
--> 583         raise RuntimeError('This event loop is already running')
    584     if events._get_running_loop() is not None:
    585         raise RuntimeError(
    586             'Cannot run the event loop while another loop is running')

RuntimeError: This event loop is already running

Expected output

The code should raise RuntimeError: My runtime error.