Apply suggestions from code review

Author: nicoddemus

changelog/12153.doc.rst

@@ -1 +1 @@
-Updated docs: Documented new way to detect if a code is running from within a pytest run
+Documented using :envvar:`PYTEST_VERSION` to detect if code is running from within a pytest run.

doc/en/example/simple.rst

@@ -413,10 +413,10 @@ running from a test you can do this:
 
 
     if os.environ.get("PYTEST_VERSION") is not None:
-        # things you want to to do if your code is called by pytest
+        # Things you want to to do if your code is called by pytest.
         ...
     else:
-        # things you want to to do if your code is not called by pytest
+        # Things you want to to do if your code is not called by pytest.
         ...