test(flac/vorbis): fix failed test caused by implicit conversion

Change to its own field instead because implicit conversion is covered
by another test.

Author: Methapon2001

lofty/tests/taglib/test_flac.rs

@@ -296,7 +296,8 @@ fn test_properties() {
 	);
 	tag.push(String::from("COMMENT"), String::from("Comment"));
 	tag.push(String::from("DATE"), String::from("2021-01-10"));
-	tag.push(String::from("DISCNUMBER"), String::from("3/5"));
+	tag.push(String::from("DISCNUMBER"), String::from("3"));
+	tag.push(String::from("DISCTOTAL"), String::from("5"));
 	tag.push(String::from("GENRE"), String::from("Genre"));
 	tag.push(String::from("ISRC"), String::from("UKAAA0500001"));
 	tag.push(String::from("LABEL"), String::from("Label 1"));