docs: remove Python version mentions from readme

Author: Molkree

test/README.md

@@ -67,7 +67,7 @@ the test for vendor_package_pairs:
 
 ## Running tests on different versions of Python
 
-Our CI currently runs tests on Python 3.7 - 3.10 under Linux.
+Our CI runs tests on all currently supported Python versions under Linux.
 
 The recommended way to do this yourself is to use python's `virtualenv`