set default for 'protected' flag

otherwise we cannot properly parse the api return value from older
versions, since that field does not exist there.

fixes sync from older versions without the protected feature

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

pbs-api-types/src/datastore.rs

@@ -396,6 +396,7 @@ pub struct SnapshotListItem {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub owner: Option<Authid>,
     /// Protection from prunes
+    #[serde(default)]
     pub protected: bool,
 }