[Spec tests] Make main link nullable for case if implementation tests don't have this one

compiler/tests-spec/testData/diagnostics/linked/declarations/classifier-declaration/classifier-initialization/testsMap.json

@@ -8,7 +8,7 @@
           "description": "Property not initialized",
           "path": "compiler/testData/diagnostics/tests/when/PropertyNotInitialized.kt",
           "unexpectedBehaviour": false,
-          "linkType": "main"
+          "linkType": "primary"
         }
       ]
     }