fix(core): prevent valid connections on same node and handle

Signed-off-by: braks <78412429+bcakmakoglu@users.noreply.github.com>

packages/core/src/composables/useHandle.ts

@@ -74,7 +74,7 @@ export const checkElementBelowIsValid = (
       result.isValid =
         (isFunction(isValidConnection)
           ? isValidConnection(connection, { edges, sourceNode: getNode(sourceId)!, targetNode: getNode(targetId)! })
-          : true) ||
+          : elementBelowNodeId !== nodeId || elementBelowHandleId !== handleId) ||
         !result.connection.target ||
         !result.connection.source
     }