tests: ignore test-qga

Commit 62c39b30 added a new test, but did not mark it for
exclusion in .gitignore.
Signed-off-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

tests/.gitignore

@@ -30,6 +30,7 @@ test-qapi-types.[ch]
 test-qapi-visit.[ch]
 test-qdev-global-props
 test-qemu-opts
+test-qga
 test-qmp-commands
 test-qmp-commands.h
 test-qmp-event