Add "mystery" as test cast to pig-latin

Slightly niche, but I did see a solution that succeeded in all the current test cases but failed for "mystery". Due to the way the logic that looks for the 'y' can be (mis)handled.

Author: petercordia

exercises/pig-latin/canonical-data.json

@@ -149,6 +149,15 @@
           },
           "expected": "erapythay"
         },
+        {
+          "uuid": ??,
+          "description": "word with y in the middle",
+          "property": "translate",
+          "input": {
+            "phrase": "mystery"
+          },
+          "expected": "ysterymay"
+        },
         {
           "uuid": "e0b3ae65-f508-4de3-8999-19c2f8e243e1",
           "description": "word beginning with thr",