pythongh-101100: Define test.regrtest module to fix references (pyt…

…honGH-112381)

Define test.regrtest module to fix references
(cherry picked from commit d525d01)

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

Doc/library/test.rst

@@ -159,6 +159,9 @@ guidelines to be followed:
 Running tests using the command-line interface
 ----------------------------------------------
 
+.. module:: test.regrtest
+   :synopsis: Drives the regression test suite.
+
 The :mod:`test` package can be run as a script to drive Python's regression
 test suite, thanks to the :option:`-m` option: :program:`python -m test`. Under
 the hood, it uses :mod:`test.regrtest`; the call :program:`python -m