PYTHON-3453 Fix handling of enterprise auth vars (#1076)

Author: blink1073

.evergreen/config.yml

@@ -494,14 +494,14 @@ functions:
         working_dir: "src"
         script: |
           cat <<EOT > prepare_enterprise_auth.sh
-          export SASL_HOST=${sasl_host}
-          export SASL_PORT=${sasl_port}
-          export SASL_USER=${sasl_user}
-          export SASL_PASS=${sasl_pass}
-          export SASL_DB=${sasl_db}
-          export PRINCIPAL=${principal}
-          export GSSAPI_DB=${gssapi_db}
-          export KEYTAB_BASE64=${keytab_base64}
+          export SASL_HOST='${sasl_host}'
+          export SASL_PORT='${sasl_port}'
+          export SASL_USER='${sasl_user}'
+          export SASL_PASS='${sasl_pass}'
+          export SASL_DB='${sasl_db}'
+          export PRINCIPAL='${principal}'
+          export GSSAPI_DB='${gssapi_db}'
+          export KEYTAB_BASE64='${keytab_base64}'
           EOT
     - command: shell.exec
       type: test