Appease clippy in Rust 1.70 (#4365)

## Issue Addressed

NA

## Proposed Changes

Fixes some new clippy lints raised after updating to Rust 1.70.

## Additional Info

NA

beacon_node/lighthouse_network/src/discovery/subnet_predicate.rs

@@ -1,4 +1,4 @@
-///! The subnet predicate used for searching for a particular subnet.
+//! The subnet predicate used for searching for a particular subnet.
 use super::*;
 use crate::types::{EnrAttestationBitfield, EnrSyncCommitteeBitfield};
 use slog::trace;