Fix passing multiple values in testenv.passenv in tox.ini (#399)

Current versions of tox advise: pass_env values cannot contain
whitespace, use comma to have multiple values in a single line

Fixes #398.

Co-authored-by: Prashant Srivastava <50466688+srprash@users.noreply.github.com>

tox.ini

@@ -43,7 +43,7 @@ envlist =
     py{37,38,39,310,311}-ext-sqlite3
 
 [testenv]
-passenv = TOXENV CI CODECOV_*
+passenv = TOXENV,CI,CODECOV_*
 
 deps =
     ; Testing packages