qapi: Ignore files created during make check

After an in-tree build and run of 'make check-{qapi-schema,unit}',
I noticed some leftover files.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Wenchao Xia <wenchaoqemu@gmail.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

tests/.gitignore

@@ -14,11 +14,14 @@ test-int128
 test-iov
 test-mul64
 test-opts-visitor
+test-qapi-event.[ch]
 test-qapi-types.[ch]
 test-qapi-visit.[ch]
 test-qdev-global-props
+test-qemu-opts
 test-qmp-commands
 test-qmp-commands.h
+test-qmp-event
 test-qmp-input-strict
 test-qmp-input-visitor
 test-qmp-marshal.c