test(NODE-5218): use debug branch from csfle

Author: durran

.evergreen/run-custom-csfle-tests.sh

@@ -36,7 +36,7 @@ pushd ../csfle-deps-tmp
 
 rm -rf libmongocrypt mongo-c-driver
 
-git clone https://github.com/mongodb/libmongocrypt.git
+git clone --branch NODE-5218 https://github.com/mongodb/libmongocrypt.git
 pushd libmongocrypt
 git fetch --tags
 git checkout "$CSFLE_GIT_REF" -b csfle-custom