doc/python: fix attr name for unittestCheckHook flags

The name should end in Array per the current conventions.

This change also contains some minor formatting fixes, as the heading
levels were inconsistent.

doc/languages-frameworks/python.section.md

@@ -744,17 +744,17 @@ work in any of the formats supported by `buildPythonPackage` currently,
 with the exception of `other` (see `format` in
 [`buildPythonPackage` parameters](#buildpythonpackage-parameters) for more details).
 
-### Using unittestCheckHook {#using-unittestcheckhook}
+#### Using unittestCheckHook {#using-unittestcheckhook}
 
 `unittestCheckHook` is a hook which will substitute the setuptools `test` command for a `checkPhase` which runs `python -m unittest discover`:
 
 ```
   nativeCheckInputs = [ unittestCheckHook ];
 
-  unittestFlags = [ "-s" "tests" "-v" ];
+  unittestFlagsArray = [ "-s" "tests" "-v" ];
 ```
 
-##### Using sphinxHook {#using-sphinxhook}
+#### Using sphinxHook {#using-sphinxhook}
 
 The `sphinxHook` is a helpful tool to build documentation and manpages
 using the popular Sphinx documentation generator.