picks the content_type of text/plain when you set is_patch to true.
https://bugzilla.mozilla.org/show_bug.cgi?id=633041
=item C<is_patch>
C<boolean> True if Bugzilla should treat this attachment as a patch.
-If you specify this, the C<content_type> should be C<text/plain>.
-(Future versions of Bugzilla will force the C<content_type> setting
-to C<text/plain> for patches and you will not have to specify it manually.)
+If you specify this, you do not need to specify a C<content_type>.
+The C<content_type of the attachment will be forced to C<text/plain>.
Defaults to False if not specified.