Bump pytest from 6.2.2 to 6.2.5

pytest 6.2.5 adds support for Python 3.10. [Link](pytest-dev/pytest#8494) to relevant PR.

tests/requirements.txt

@@ -1,6 +1,6 @@
 coverage==5.4
 pygments==2.7.4
-pytest==6.2.2
+pytest==6.2.5
 pytest-cov==2.11.1
 pytest-asyncio==0.14.0
 pytest-mock==3.5.1