Fix the qlpack json schema

This schema was incorrectly tagging `defaultSuite` properties that
aren't arrays as errors.

I think there are more, similar errors in this schema, but I only fixed
this one so that I can get `github/semmle-code` working with test
discovery.

Author: aeisenberg

extensions/ql-vscode/src/packaging/qlpack-file.schema.json

@@ -51,6 +51,9 @@
                 "$ref": "#/definitions/SuiteInstruction"
               }
             },
+            {
+              "$ref": "#/definitions/SuiteInstruction"
+            },
             {
               "type": "null"
             }