Revert renaming extension tests (#5473)

* Split py_version_35 test

Author: cdce8p

tests/functional/ext/code_style/consider_using_assignment_expr.py renamed to tests/functional/ext/code_style/cs_consider_using_assignment_expr.py

@@ -0,0 +1,7 @@
+"""No warnings should be emitted for features that require Python > 3.5"""
+# pylint: disable=invalid-name
+
+# consider-using-assignment-expr -> requires Python 3.8
+a1 = 2
+if a1:
+    ...