Let find_package(executorch) find the correct include directory (#6102)

Summary:
There's a typo in `executorch-wheel-config.cmake` that points to the wrong `include` path:
```
<site-packages>/executorch/share/cmake/include
```

Where it actually should be
```
<site-packages>/executorch/include
```

Fixing this issue. Verified it on [build_torchao_ops.sh](https://github.com/pytorch/ao/blob/main/torchao/experimental/build_torchao_ops.sh)

Pull Request resolved: #6102

Reviewed By: lucylq

Differential Revision: D64189337

Pulled By: larryliu0820

fbshipit-source-id: 13033587f5499537623995b8f9457fb47d780340

Author: larryliu0820

build/executorch-wheel-config.cmake

@@ -31,7 +31,7 @@ if(_portable_lib_LIBRARY)
   message(STATUS "ExecuTorch portable library is found at ${_portable_lib_LIBRARY}")
   list(APPEND EXECUTORCH_LIBRARIES _portable_lib)
   add_library(_portable_lib STATIC IMPORTED)
-  set(EXECUTORCH_INCLUDE_DIRS ${CMAKE_CURRENT_LIST_DIR}/include)
+  set(EXECUTORCH_INCLUDE_DIRS ${CMAKE_CURRENT_LIST_DIR}/../../include)
   set_target_properties(_portable_lib PROPERTIES
     IMPORTED_LOCATION "${_portable_lib_LIBRARY}"
     INTERFACE_INCLUDE_DIRECTORIES "${EXECUTORCH_INCLUDE_DIRS}"