Use snippet anchor instead of line range

snippets/rust/src/static_channel_backup.rs

@@ -2,9 +2,11 @@ use anyhow::Result;
 use breez_sdk_core::*;
 
 async fn retrieve_backup_files() -> Result<()> {
+    // ANCHOR: static-channel-backup
     let backup_data = BreezServices::static_backup(StaticBackupRequest {
         working_dir: "<working directory>".into(),
     })?;
+    // ANCHOR_END: static-channel-backup
 
     Ok(())
 }