feat: implement change timestamp for subscriptions set

src/server/gpodder/simple/subscriptions.rs

@@ -85,8 +85,11 @@ pub async fn put_device_subscriptions(
             .insert(&ctx.pool)?
         };
 
-        Ok::<_, AppError>(db::Subscription::update_for_device(
-            &ctx.pool, device.id, urls,
+        Ok::<_, AppError>(db::Subscription::set_for_device(
+            &ctx.pool,
+            device.id,
+            urls,
+            chrono::Utc::now().timestamp(),
         )?)
     })
     .await