[calls] call: Add transfer annotation for get_protocol()

[Evangelos Ribeiro Tzaras <devrtz src gnome org>]

commit 500581d35dc27725c84cb69b4c1ea627e25dcffd
Author: Evangelos Ribeiro Tzaras <devrtz fortysixandtwo eu>
Date:   Fri Jan 21 10:06:44 2022 +0100

    call: Add transfer annotation for get_protocol()

 src/calls-call.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/calls-call.c b/src/calls-call.c
index 6197d800..c127a391 100644
--- a/src/calls-call.c
+++ b/src/calls-call.c
@@ -469,7 +469,7 @@ calls_call_get_inbound (CallsCall *self)
  *
  * Get the protocol of the call (i.e. "tel", "sip")
  *
- * Returns: The protocol used or %NULL when unknown
+ * Returns: (transfer none): The protocol used or %NULL when unknown
  */
 const char *
 calls_call_get_protocol (CallsCall *self)