test(NODE-3713): check csfle node install

Author: durran

.evergreen/run-tests.sh

@@ -41,7 +41,9 @@ if [[ -z "${CLIENT_ENCRYPTION}" ]]; then
   unset AWS_ACCESS_KEY_ID;
   unset AWS_SECRET_ACCESS_KEY;
 else
-  npm install mongodb-client-encryption@">=2.0.0-beta.0"
+  if [[ ! -d ${PROJECT_DIRECTORY}/node_modules/mongodb-client-encryption ]]; then
+    npm install mongodb-client-encryption@">=2.0.0-beta.0"
+  fi
   pip install --upgrade boto3
 
   # Get access to the AWS temporary credentials: