Update parity-scale-codec to prepare for breaking rustc release (#6746)

This updates parity-scale-codec{-derive} to prepare for a rustc release
that would otherwise break the derive implementation:
rust-lang/rust#73084

Author: bkchr

Cargo.toml

@@ -14,7 +14,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 [dependencies]
 sp-authority-discovery = { version = "2.0.0-rc5", default-features = false, path = "../../primitives/authority-discovery" }
 sp-application-crypto = { version = "2.0.0-rc5", default-features = false, path = "../../primitives/application-crypto" }
-codec = { package = "parity-scale-codec", version = "1.3.1", default-features = false, features = ["derive"] }
+codec = { package = "parity-scale-codec", version = "1.3.4", default-features = false, features = ["derive"] }
 sp-std = { version = "2.0.0-rc5", default-features = false, path = "../../primitives/std" }
 serde = { version = "1.0.101", optional = true }
 pallet-session = { version = "2.0.0-rc5", features = ["historical" ], path = "../session", default-features = false }