Update cert-renewer@.service

Wrap command line env variables in braces so they are treated as a single argument (rather than split on whitespace)

systemd/cert-renewer@.service

@@ -15,10 +15,10 @@ Environment=STEPPATH=/etc/step-ca \
 ; ExecCondition checks if the certificate is ready for renewal,
 ; based on the exit status of the command.
 ; (In systemd 242 or below, you can use ExecStartPre= here.)
-ExecCondition=/usr/bin/step certificate needs-renewal $CERT_LOCATION
+ExecCondition=/usr/bin/step certificate needs-renewal ${CERT_LOCATION}
 
 ; ExecStart renews the certificate, if ExecStartPre was successful.
-ExecStart=/usr/bin/step ca renew --force $CERT_LOCATION $KEY_LOCATION
+ExecStart=/usr/bin/step ca renew --force ${CERT_LOCATION} ${KEY_LOCATION}
 
 ; Try to reload or restart the systemd service that relies on this cert-renewer
 ; If the relying service doesn't exist, forge ahead.