Fix typo on inline comment for email.generator (GH-98210)

Trivial change to comment - no issue or new entry necessary

Lib/email/generator.py

@@ -170,7 +170,7 @@ def _write(self, msg):
         # parameter.
         #
         # The way we do this, so as to make the _handle_*() methods simpler,
-        # is to cache any subpart writes into a buffer.  The we write the
+        # is to cache any subpart writes into a buffer.  Then we write the
         # headers and the buffer contents.  That way, subpart handlers can
         # Do The Right Thing, and can still modify the Content-Type: header if
         # necessary.