Minor changes to be aligned with code

tests/features/Vendor Extensibility/vendor_extensibility.robot

@@ -184,8 +184,8 @@ Publish API with vendorExt active but without vendorSpecifics
     ...    ProblemDetails
     ...    title=Bad Request
     ...    status=400
-    ...    detail=VendorExt feature active at Supported Features but VendorSpecifics parameters not published
-    ...    cause=VendorExt feature active but vendorSpecifics not present
+    ...    detail=If and only if VendorExt feature is enabled, then vendor-specific fields should be defined
+    ...    cause=Vendor extensibility misconfiguration
 
 Publish API with vendorExt inactive but with vendorSpecifics
     [Tags]    vendor_extensibility-5
@@ -220,8 +220,8 @@ Publish API with vendorExt inactive but with vendorSpecifics
     ...    ProblemDetails
     ...    title=Bad Request
     ...    status=400
-    ...    detail=VendorExt feature inactive at Supported Features but VendorSpecifics are present parameters published
-    ...    cause=VendorExt feature inactive but vendorSpecifics present
+    ...    detail=If and only if VendorExt feature is enabled, then vendor-specific fields should be defined
+    ...    cause=Vendor extensibility misconfiguration
 
 Published API without vendor extensibility discover with VendSpecQueryParams enabled
     [Tags]    vendor_extensibility-6
@@ -331,5 +331,5 @@ Publish API without supportedFeatures
     ...    ProblemDetails
     ...    title=Bad Request
     ...    status=400
-    ...    detail=supportedFeatures must be present in this request
-    ...    cause=supportedFeatures missed
+    ...    detail=supportedFeatures not present in request
+    ...    cause=supportedFeatures not present