Memory leak in calls_call_window_add_call

https://source.puri.sm/Librem5/calls/blob/e04fa0aeb6e79f2aa58015995166df0d4ef7728e/src/calls-call-window.c#L255

holder is being leaked here because g_list_store_append() (below) adds its own reference

Copied from !18 (comment 7364)