legacy-cgi is required for coreapi if Python>=3.13 (#9817)

> module is no longer part of the Python standard library. It was removed in Python 3.13 after being deprecated in Python 3.11. The removal was decided in PEP 594.

https://docs.python.org/3/library/cgi.html

Author: ulgens

requirements/requirements-optionals.txt

@@ -4,6 +4,7 @@ coreschema==0.0.4
 django-filter
 django-guardian>=2.4.0,<2.5
 inflection==0.5.1
+legacy-cgi; python_version>="3.13"
 markdown>=3.3.7
 psycopg[binary]>=3.1.8
 pygments~=2.17.0