turn on run whole graph to pass all test cases

tests/test-backend-ops.cpp

@@ -4909,6 +4909,11 @@ struct test_conv_2d : public test_case {
         return 5e-4;
     }
 
+    // must run the whole graph for all test cases to pass
+    bool run_whole_graph() override {
+        return true;
+    }
+
     uint64_t op_flops(ggml_tensor * t) override {
         GGML_UNUSED(t);
         // Just counting matmul costs: