Our old subversion does not seem to support the expiration of letsencrypt root certificate, as we can see in tests:

ClientError: ("Unable to connect to a repository at URL 'https://svn.erp5.org/repos/public/erp5/trunk/bt5/test_web'\nServer SSL certificate verification failed: certificate has expired", [("Unable to connect to a repository at URL 'https://svn.erp5.org/repos/public/erp5/trunk/bt5/test_web'", 230001), ('Server SSL certificate verification failed: certificate has expired', 230001)])

This is also what we observe when using svn command from ERP5 software release:

~/srv/slapos/shared/subversion/26833ca5dbfd6944dc2e584d0761dc89/bin/svn info https://svn.erp5.org/repos/public/erp5/trunk/bt5/test_web
Error validating server certificate for 'https://svn.erp5.org:443':
 - The certificate has expired.
Certificate information:
 - Hostname: svn.erp5.org
 - Valid: from Sep 26 05:47:35 2021 GMT until Dec 25 05:47:34 2021 GMT
 - Issuer: Let's Encrypt, US
 - Fingerprint: 01:98:FF:1B:68:A1:55:59:35:EE:1C:57:8A:6E:5A:22:1F:3E:B2:86
(R)eject, accept (t)emporarily or accept (p)ermanently? ^Csvn: E200015: Unable to connect to a repository at URL 'https://svn.erp5.org/repos/public/erp5/trunk/bt5/test_web'

Updating subversion and linking it with openssl 1.1 seem to solve the issue.