Update asserted OpenAPI documents to use "enum" instead of "default"

Author: commonsensesoftware

src/AspNetCore/WebApi/test/Asp.Versioning.OpenApi.Tests/Content/v1-minimal.json

@@ -38,7 +38,7 @@
             "required": true,
             "schema": {
               "type": "string",
-              "default": "1.0"
+              "enum": [ "1.0" ]
             }
           }
         ],

src/AspNetCore/WebApi/test/Asp.Versioning.OpenApi.Tests/Content/v1-mixed.json

@@ -38,7 +38,7 @@
             "required": true,
             "schema": {
               "type": "string",
-              "default": "1.0"
+              "enum": [ "1.0" ]
             }
           }
         ],
@@ -93,7 +93,7 @@
             "required": true,
             "schema": {
               "type": "string",
-              "default": "1.0"
+              "enum": [ "1.0" ]
             }
           }
         ],

src/AspNetCore/WebApi/test/Asp.Versioning.OpenApi.Tests/Content/v1.json

@@ -40,7 +40,7 @@
             "required": true,
             "schema": {
               "type": "string",
-              "default": "1.0"
+              "enum": ["1.0"]
             }
           }
         ],