Bump pytest-asyncio dependency (#3369)

* Bump pytest-asyncio dependency

* Add newsfragment for pytest-asyncio bump

Author: kclowes

newsfragments/3369.internal.rst

@@ -0,0 +1 @@
+Increase python-asyncio dependency to be >=0.21.2,<0.23

setup.py

@@ -20,7 +20,7 @@
         "flaky>=3.7.0",
         "hypothesis>=3.31.2",
         "pre-commit>=3.4.0",
-        "pytest-asyncio>=0.18.1,<0.23",
+        "pytest-asyncio>=0.21.2,<0.23",
         "pytest-mock>=1.10",
         "pytest-watch>=4.2",
         "pytest-xdist>=1.29",