Merge branch '64870-can-t-save-pages-domain-form-with-let-s-encrypt-enabled-if-current-certificate-is-outdated' into 'master'

Resolve "Can't save pages domain form with Let's Encrypt enabled if current certificate is outdated"

Closes #64870

See merge request gitlab-org/gitlab-ce!30995

(cherry picked from commit 8073b055)

9c0f4286 Validate certificate chain only if it's changed