emcmake breaks CMAKE_PREFIX_PATH

If I use emcmake, `CMAKE_PREFIX_PATH` breaks. For example, the following CMake file:

```cmake
cmake_minimum_required(VERSION 3.15...3.26)

project(CMCheck LANGUAGES CXX)

list(APPEND CMAKE_PREFIX_PATH "${CMAKE_CURRENT_SOURCE_DIR}/pre")

find_package(CheckMe CONFIG REQUIRED)
```

And the following file in `pre/CheckMeConfig.cmake`:

```cmake
message(STATUS "Found correctly")
```

Produces the expected message if run on the host CMake, but when run through emcmake, it produces:

```console
$ emcmake cmake -S . -B build
configure: cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=/emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR=/emsdk/node/15.14.0_64bit/bin/node;--experimental-wasm-bulk-memory;--experimental-wasm-threads
CMake Error at CMakeLists.txt:7 (find_package):
Could not find a package configuration file provided by "CheckMe" with any
of the following names:

CheckMeConfig.cmake
checkme-config.cmake

Add the installation prefix of "CheckMe" to CMAKE_PREFIX_PATH or set
"CheckMe_DIR" to a directory containing one of the above files. If
"CheckMe" provides a separate development package or SDK, be sure it has
been installed.

-- Configuring incomplete, errors occurred
```

Is this expected? A bug with CMake I should report there, like faulty platform logic? Setting `CheckMe_DIR` works.

**Version of emscripten/emsdk:**

```
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.32 (eab98adf462c39f3c31d348331c4830bcaa36949)
clang version 17.0.0 (https://github.com/llvm/llvm-project df82394e7a2d06506718cafa347bf7827c79fc4f)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /emsdk/upstream/bin
```

`CMAKE_FIND_USE_CMAKE_PATH` and `CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH` are not set to false.

(This is breaking the CMake based Python build backends scikit-build-core in Pyodide, which discovers the header only pybind11 via this method, FYI)