Set caps on the harness in tests before pushing the first buffer

Otherwise there will be warnings about data flow before segment events,
as harness is only sending the segment event together with the caps.

gst-plugin-closedcaption/tests/mcc_parse.rs

@@ -50,6 +50,8 @@ fn test_parse() {
 
     let mut h = gst_check::Harness::new("mccparse");
 
+    h.set_src_caps_str("application/x-mcc, version=(int) 1");
+
     let mut input_len = 0;
     let mut output_len = 0;
     let mut checksum = 0u32;

gst-plugin-threadshare/tests/udpsrc.rs

@@ -133,6 +133,7 @@ fn test_socket_reuse() {
         udpsink.set_property("port", &6001i32).unwrap();
     }
     sink_h.play();
+    sink_h.set_src_caps_str("application/test");
 
     {
         let udpsrc = ts_src_h2.get_element().unwrap();