Document that the passenv environment setting is case insensitive (#1723)

* Document that the passenv environment setting is case insensitive

* review feedback

Author: gnikonorov

CONTRIBUTORS

@@ -36,6 +36,7 @@ Florian Bruhin
 Florian Preinstorfer
 Florian Schulze
 George Alton
+Gleb Nikonorov
 Gonéri Le Bouder
 Hazal Ozturk
 Henk-Jaap Wagenaar

docs/changelog/1534.doc.rst

@@ -0,0 +1 @@
+Document that the ``passenv`` environment setting is case insensitive. - by :user:`gnikonorov`

docs/config.rst

@@ -421,7 +421,9 @@ Complete list of settings that you can put into ``testenv*`` sections:
     environment when executing test commands.  If a specified environment
     variable doesn't exist in the tox invocation environment it is ignored.
     You can use ``*`` and ``?`` to match multiple environment variables with
-    one name.
+    one name. The list of environment variable names is not case sensitive, and
+    all variables that match when upper cased will be passed. For example, passing
+    ``A`` will pass both ``A`` and ``a``.
 
     Some variables are always passed through to ensure the basic functionality
     of standard library functions or tooling like pip: