bracket-push: Add test case "partially paired brackets" (#1219)

Guard against solutions returning `true` once brackets are matched, which will pass all previous tests but the added one

Author: mrcfps

exercises/bracket-push/canonical-data.json

@@ -1,6 +1,6 @@
 {
   "exercise": "bracket-push",
-  "version": "1.2.0",
+  "version": "1.3.0",
   "cases": [
     {
       "description": "paired square brackets",
@@ -50,6 +50,14 @@
       },
       "expected": true
     },
+    {
+      "description": "partially paired brackets",
+      "property": "isPaired",
+      "input": {
+        "value": "{[])"
+      },
+      "expected": false
+    },
     {
       "description": "simple nested brackets",
       "property": "isPaired",