CMake configuration error with user provided OpenVDB

If the user provides OpenVDB package prior including lagrange, it will trigger an error during CMake configuration step (version 3.31.6)

```
[cmake] CMake Error at build/_deps/lagrange-src/cmake/lagrange/lagrange_find_package.cmake:48 (target_link_libraries):
[cmake] Cannot specify link libraries for target "OpenVDB::openvdb" which is not
[cmake] built by this project.
```

from lines

https://github.com/adobe/lagrange/blob/b3f4080cf039c043d7024a78b0a3e42ea1379dec/cmake/lagrange/lagrange_find_package.cmake#L44-L49

because it seems `GLOBAL` target allows for modifying properties of the imported target.

> https://cmake.org/cmake/help/latest/command/find_package.html#basic-signature
> Added in version 3.24: Specifying the GLOBAL keyword will promote all imported targets to a global scope in the importing project. Alternatively, this functionality can be enabled by setting the [CMAKE_FIND_PACKAGE_TARGETS_GLOBAL](https://cmake.org/cmake/help/latest/variable/CMAKE_FIND_PACKAGE_TARGETS_GLOBAL.html#variable:CMAKE_FIND_PACKAGE_TARGETS_GLOBAL) variable.

The minimal reproducing example is

```cmake
cmake_minimum_required(VERSION 3.31)

if(DEFINED ENV{VCPKG_ROOT})
set(CMAKE_TOOLCHAIN_FILE "$ENV{VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake" CACHE STRING "")
endif()

project(test_lagrange VERSION 0.1.0 LANGUAGES C CXX)

find_package(OpenVDB CONFIG REQUIRED)
# find_package(OpenVDB CONFIG REQUIRED GLOBAL) # Workaround

include(FetchContent)
FetchContent_Declare(lagrange GIT_REPOSITORY https://github.com/adobe/lagrange.git GIT_TAG v6.34.0 GIT_SHALLOW TRUE)
FetchContent_MakeAvailable(lagrange)

lagrange_include_modules(volume)
```

Actually, I wonder what is the "right" CMake way around `find_package` with GLOBAL or not. It seems that there is even a [CMake default option](https://cmake.org/cmake/help/latest/variable/CMAKE_FIND_PACKAGE_TARGETS_GLOBAL.html) to put them all GLOBAL but off by default.

To make is work without the user knowing might be wrapping (all) `find_package` in `lagrange_find_package` by `if(NOT TARGET) ... endif()`