$ ./python -m test -vuall test_asyncio
...
======================================================================
FAIL: test_run_keeps_context (test.test_asyncio.test_runners.RunnerTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/test/test_asyncio/test_runners.py", line 299, in test_run_keeps_context
    self.assertEqual({cvar: 2}, dict(runner.run(get_context())))
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: {<Con[47 chars]0>: 2} != {<Con[47 chars]0>: 2, <ContextVar name='decimal_context' at 0[164 chars]ow])}
- {<ContextVar name='cvar' default=-1 at 0x7f729c70e740>: 2}
?                                                          ^

+ {<ContextVar name='cvar' default=-1 at 0x7f729c70e740>: 2,
?                                                          ^

+  <ContextVar name='decimal_context' at 0x7f729d60e7b0>: Context(prec=28, rounding=ROUND_HALF_EVEN, Emin=-999999, Emax=999999, capitals=1, clamp=0, flags=[], traps=[InvalidOperation, DivisionByZero, Overflow])}

----------------------------------------------------------------------


When run the test separately it passes successfully.

Thanks for the report!
I read it ad 'decimal context tests modifies the environment'.
I'll update asyncio runner test to ignore external contextvars.

New changeset 20e6e5636a06fe5e1472062918d0a302d82a71c3 by Andrew Svetlov in branch 'main':
bpo-47118: Fix asyncio.Runner tests error (32117)
https://github.com/python/cpython/commit/20e6e5636a06fe5e1472062918d0a302d82a71c3