ReAwaitable does not support concurrent await call

# Bug report ## What's wrong ReAwaitable cannot be awaited from multiple asyncio tasks simultaneously, and raises exception. ``` <user>/Library/Caches/pypoetry/virtualenvs/project-env/bin/python /Applications/PyCharm.app/Contents/plugins/python-ce/helpers/pycharm/_jb_pytest_runner.py --target test_reawaitable_concurrency.py::test_concurrent_awaitable Testing started at 16:14 ... Launching pytest with arguments test_reawaitable_concurrency.py::test_concurrent_awaitable --no-header --no-summary -q in <user>/repos/project/tests/test_primitives/test_reawaitable ============================= test session starts ============================== collecting ... collected 2 items Running 2 items in this shard: tests/test_primitives/test_reawaitable/test_reawaitable_concurrency.py::test_concurrent_awaitable[trio], tests/test_primitives/test_reawaitable/test_reawaitable_concurrency.py::test_concurrent_awaitable[asyncio] test_reawaitable_concurrency.py::test_concurrent_awaitable[trio] test_reawaitable_concurrency.py::test_concurrent_awaitable[asyncio] <user>/Library/Caches/pypoetry/virtualenvs/project-env/lib/python3.12/site-packages/coverage/inorout.py:524: CoverageWarning: Module project was previously imported, but not measured (module-not-measured) self.warn(msg, slug="module-not-measured") ERROR: Coverage failure: total of 1 is less than fail-under=100 ============================== 2 failed in 1.29s =============================== FAILED [ 50%] tests/test_primitives/test_reawaitable/test_reawaitable_concurrency.py:10 (test_concurrent_awaitable[trio]) + Exception Group Traceback (most recent call last): | File "<user>/Library/Caches/pypoetry/virtualenvs/project-env/lib/python3.12/site-packages/_pytest/runner.py", line 341, in from_call | result: TResult | None = func() | ^^^^^^ [...multiple frames omitted for brevity...] | File "<user>/repos/project/tests/test_primitives/test_reawaitable/test_reawaitable_concurrency.py", line 17, in test_concurrent_awaitable | async with anyio.create_task_group() as tg: | ^^^^^^^^^^^^^^^^^^^^^^^^^ | File "<user>/Library/Caches/pypoetry/virtualenvs/project-env/lib/python3.12/site-packages/anyio/_backends/_trio.py", line 191, in __aexit__ | return await self._nursery_manager.__aexit__(exc_type, exc_val, exc_tb) | ExceptionGroup: Exceptions from Trio nursery (1 sub-exception) +-+---------------- 1 ---------------- | Traceback (most recent call last): | File "<user>/repos/project/tests/test_primitives/test_reawaitable/test_reawaitable_concurrency.py", line 16, in await_reawaitable | return await reawaitable | ^^^^^^^^^^^^^^^^^ | File "<user>/repos/project/project/primitives/reawaitable.py", line 109, in _awaitable | self._cache = await self._coro | ^^^^^^^^^^^^^^^^ | RuntimeError: coroutine is being awaited already +------------------------------------ FAILED [100%] [... similar traceback omitted for brevity ...] <user>/Library/Caches/pypoetry/virtualenvs/project-env/lib/python3.12/site-packages/pytest_cov/plugin.py:355: CovFailUnderWarning: Coverage failure: total of 1 is less than fail-under=100 warnings.warn(CovFailUnderWarning(message), stacklevel=1) ``` ## How is that should be ReAwaitable should be awaitable from multiple simultaneous tasks. ## System information - `returns` version: 0.25.0 - `pytest` version (if any): 8.3.4