Update Rust crate tokio to 1.51.0

Author: oxide-renovate[bot]

Cargo.lock

@@ -15,5 +15,5 @@ ruma = { version = "0.14", features = ["events"] }
 ruma-common = "0.17.0"
 serde = { version = "1.0.228", features = ["derive"] }
 thiserror = "2.0.17"
-tokio = "1.48.0"
+tokio = "1.51.0"
 tracing = "0.1.44"