matrix-backup-borg: fix wording in defaults/main.yml comment

roles/matrix-backup-borg/defaults/main.yml

@@ -44,7 +44,7 @@ matrix_backup_borg_location_repositories: []
 # exclude following paths:
 matrix_backup_borg_location_exclude_patterns: []
 
-# borg encryption mode, only repokey-* is supported
+# borg encryption mode, only "repokey-*" and "none" are supported
 matrix_backup_borg_encryption: repokey-blake2
 
 # private ssh key used to connect to the borg repo