fix: stderr noise (#7346)

Author: michaelneale

crates/goose-cli/src/session/output.rs

@@ -261,7 +261,7 @@ pub fn render_message(message: &Message, debug: bool) {
                 }
             }
             _ => {
-                println!("WARNING: Message content type could not be rendered");
+                eprintln!("WARNING: Message content type could not be rendered");
             }
         }
     }
@@ -349,7 +349,7 @@ pub fn render_message_streaming(
             }
             _ => {
                 flush_markdown_buffer(buffer, theme);
-                println!("WARNING: Message content type could not be rendered");
+                eprintln!("WARNING: Message content type could not be rendered");
             }
         }
     }