write test against regression of syntax check_literal_as_filter

check_literal_as_filter returned literals at the end of pipelines too, which isn't
desirable since that's the job of check_literal_as_sink

src/syntax/check/test.rs

@@ -49,6 +49,14 @@ fn test_check_literal_as_filter() {
     )
 }
 
+#[test]
+fn test_check_literal_as_filter_positive_on_sink() {
+    let test_data = "meow | 42";
+    let syntax = parse_syntax(test_data).unwrap();
+
+    assert_eq!(check_literal_as_filter(&syntax), Ok(()))
+}
+
 #[test]
 fn test_check_literal_with_args() {
     let test_data = "14 12 | sink";