addons: letsencrypt: propagation_seconds setting is not honored

Hi !

It looks like the DNS propagation seconds setting of letsencrypt is not honored :

[18:37:42] INFO: Selected DNS Provider: dns-ovh
[18:37:42] INFO: Use propagation seconds: 120
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator dns-ovh, Installer None
Obtaining a new certificate
Performing the following challenges:
dns-01 challenge for <REDACTED>
Waiting 30 seconds for DNS changes to propagate
Waiting for verification...
Challenge failed for domain <REDACTED>
dns-01 challenge for <REDACTED>
Cleaning up challenges
Some challenges have failed.
IMPORTANT NOTES:
 - The following errors were reported by the server:
   Domain: <REDACTED>
   Type:   dns
   Detail: DNS problem: NXDOMAIN looking up TXT for
   _acme-challenge.<REDACTED> - check that a DNS record exists
   for this domain

Thanks for your consideration 😃