test: 3.11.0b3 is out, so remove the workaround

Author: nedbat

setup.cfg

@@ -2,9 +2,7 @@
 # For details: https://github.com/nedbat/coveragepy/blob/master/NOTICE.txt
 
 [tool:pytest]
-# Use --assert=plain since 3.11.0b2 has a bug: https://github.com/pytest-dev/pytest/issues/10008
-# fixed by https://github.com/python/cpython/pull/93359
-addopts = -q -n auto --strict-markers --no-flaky-report -rfEX --failed-first --assert=plain
+addopts = -q -n auto --strict-markers --no-flaky-report -rfEX --failed-first
 python_classes = *Test
 markers =
     expensive: too slow to run during "make smoke"