Add a constraint for #221 to error on bad group-as

This new constraint implements a check for the following issue comment.

metaschema-framework/metaschema-java#221 (comment)

schema/metaschema/metaschema-module-constraints.xml

@@ -46,6 +46,11 @@
                 <description>Ensure each import is a Metaschema module.</description>
                 <message>Unable the resource at '{{ resolve-uri(@href) }}' is not a Metaschema module.</message>
             </expect>
+            <expect id="module-model-group-as-in-json-invalid" target=".//(define-assembly|define-field|assembly|field)[@max-occurs=1]" test=".[not(group-as)]">
+                <formal-name>Group-As Behavior Used with Valid Max-Occurs</formal-name>
+                <description>Given group-as behavior for a parent assembly or field, you cannot have a group-as for multiple values.</description>
+                <message>The group-as for the parent location requires a max-occurs that is greater than 1 to support that feature.</message>
+            </expect>
         </constraints>
     </context>
     <context>