gstreamer: ignore cognitive_complexity warnings

Those are just long tests.

gstreamer/src/buffer.rs

@@ -1118,6 +1118,7 @@ mod tests {
     }
 
     #[test]
+    #[allow(clippy::cognitive_complexity)]
     fn test_memories() {
         ::init().unwrap();
 

gstreamer/src/buffer_cursor.rs

@@ -437,6 +437,7 @@ mod tests {
     use super::*;
 
     #[test]
+    #[allow(clippy::cognitive_complexity)]
     fn test_buffer_cursor() {
         use std::io::{self, Read, Seek, Write};
 
@@ -528,6 +529,7 @@ mod tests {
     }
 
     #[test]
+    #[allow(clippy::cognitive_complexity)]
     fn test_buffer_cursor_ref() {
         use std::io::{self, Read, Seek, Write};