Fix inplace predict with fallback when base margin is used. (#9536)

- Copy meta info from proxy DMatrix.
- Use `std::call_once` to emit less warnings.

src/data/proxy_dmatrix.cc

@@ -55,6 +55,7 @@ std::shared_ptr<DMatrix> CreateDMatrixFromProxy(Context const *ctx,
   }
 
   CHECK(p_fmat) << "Failed to fallback.";
+  p_fmat->Info() = proxy->Info().Copy();
   return p_fmat;
 }
 }  // namespace xgboost::data