schemas: add missing vim modeline

Similar to f7160f3218 "schemas: Add vim modeline"

Signed-off-by: Victor Toso <victortoso@redhat.com>
Message-Id: <20211220145624.52801-1-victortoso@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/qapi/compat.json b/qapi/compat.json
index dd7261a..c53b69f 100644
--- a/qapi/compat.json
+++ b/qapi/compat.json
@@ -1,4 +1,5 @@
 # -*- Mode: Python -*-
+# vim: filetype=python
 
 ##
 # = Compatibility policy