PYTHON-3413 Ensure AWS EC2 Credential Test is Running Properly (#1048)

.evergreen/config.yml

@@ -643,6 +643,13 @@ functions:
         working_dir: "src"
         script: |
           ${PREPARE_SHELL}
+          if [ "${skip_EC2_auth_test}" = "true" ]; then
+             echo "This platform does not support the EC2 auth test, skipping..."
+             exit 0
+          fi
+          # Write an empty prepare_mongodb_aws so no auth environment variables
+          # are set.
+          echo "" > "${PROJECT_DIRECTORY}/prepare_mongodb_aws.sh"
           PYTHON_BINARY=${PYTHON_BINARY} ASSERT_NO_URI_CREDS=true .evergreen/run-mongodb-aws-test.sh
 
   "run aws auth test with aws credentials as environment variables":