Add test to opcodes

Cargo mutant found a mutant in opcodes.

Add a test to kill it.

primitives/src/opcodes.rs

@@ -565,6 +565,12 @@ mod tests {
         assert_eq!(s, "    OP_NOP");
     }
 
+    #[test]
+    fn ordinary_op_code() {
+        let ordinary_op = Ordinary::from_opcode(OP_PUSHDATA1).expect("0x4C");
+        assert_eq!(ordinary_op.to_u8(), 0x4C_u8);
+    }
+
     #[test]
     fn decode_pushnum() {
         // Test all possible opcodes