Add explanation for tox.ini olddriver change

Author: sfc-gh-pmansour

tox.ini

@@ -86,6 +86,8 @@ skip_install = True
 setenv = {[testenv]setenv}
 passenv = {[testenv]passenv}
 commands =
+    # Unit and pandas tests are already skipped for the old driver (see test/conftest.py). Avoid walking those
+    # directories entirely to avoid loading any potentially incompatible subdirectories' own conftest.py files.
     {env:SNOWFLAKE_PYTEST_CMD} --ignore=test/unit --ignore=test/pandas -m "not skipolddriver" -vvv {posargs:} test
 
 [testenv:noarrowextension]