Exclude testapp submodules from built packages

The controls in `MANIFEST.in` are unfortunately neither necessary
nor sufficient to control the inclusion of files from the 'testapp'
directory in wheels built from the original source. Those are
instead controlled by the packages listed in `setup.py`, as found
by `find_packages`.

It is unclear to me why `find_packages` requires explicitly excluding
both 'testapp' and 'testapp*' (either spelling on its own isn't
sufficient to exclude both files in the 'testapp' folder as well
as those within subfolders), however from testing this combination
has the desired effect.

In theory this commit could remove the exclusion from `MANIFEST.in`,
allowing the test files to be included in the source distribution
now that they are fully excluded from the installed files, however
it is the maintainer's preference that the files also be completely
excluded from the source distribution too, so that is left unchanged.

Tested by manually installing locally built source and wheel
distribution packages and verifying what files were included within
'site-pacakges'.

Fixes jrief#359

Author: PeterJCLaw

setup.py

@@ -47,7 +47,7 @@ def readfile(filename):
     install_requires=[
         'Django>=4.0',
     ],
-    packages=find_packages(exclude=['client', 'testapp', 'docs']),
+    packages=find_packages(exclude=['client', 'testapp', 'testapp*', 'docs']),
     include_package_data=True,
     zip_safe=False,
 )