pythongh-101100: Define test.regrtest module to fix references (python#112381)

Define test.regrtest module to fix references

Author: hugovk

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