bpo-41748: Handles unquoted attributes with commas (GH-24072)

bpo-41748: Handles unquoted attributes with commas (GH-24072)

* bpo-41748: Adds tests for unquoted attributes with comma

* bpo-41748: Handles unquoted attributes with comma

* bpo-41748: Addresses review comments

* bpo-41748: Addresses review comments

* Adds more test cases
* Simplifies the regex for handling spaces

* bpo-41748: Moves attributes tests under the right class

* bpo-41748: Addresses review about duplicate attributes

* bpo-41748: Adds NEWS.d entry for this patch
(cherry picked from commit 9eb11a139fac5514d8456626806a68b3e3b7eafb)

Co-authored-by: Karl Dubost <karl+github@la-grange.net>