MONGOCRYPT-951: Pin cmake to 4.3.4

[prestonvasquez]

MONGOCRYPT-951

Pin to avoid issue in parent task while investigating the following error from the cmake 4.4.0 release:

CMake Error: The warning category "error -DCMAKE_CXX_LINK_EXECUTABLE='echo not linking now...'" is not known.
CMake Error at cmake-build/_deps/embedded_mcd-src/src/libmongoc/CMakeLists.txt:425 (TRY_COMPILE):
  Failed to configure test project build system.
Call Stack (most recent call first):
  cmake-build/_deps/embedded_mcd-src/src/libmongoc/CMakeLists.txt:449 (mongoc_get_accept_args)

[kevinAlbs]

Thank you for the fix.