tests: add test case for better coverage of xorpattern modifier.

Author: plusvic

lib/src/tests/mod.rs

@@ -2703,6 +2703,7 @@ fn match_length() {
 #[test]
 fn xor() {
     pattern_true!(r#""mississippi" xor"#, b"mississippi");
+    pattern_false!(r#""mississippi" xor"#, b"mississippp");
     pattern_true!(r#""mississippi" xor"#, b"lhrrhrrhqqh");
     pattern_false!(r#""mississippi" xor"#, b"lhrrhrrhqqq");
     pattern_true!(r#""ssi" xor"#, b"lhrrhrrhqqh");