Update to SCALE 1.2.0 (#5113)

This updates `parity-scale-codec` to `1.2.0`, which includes multiple
performance improvements and a fix that bounds the capacity of a vector
at decoding.

substrate/utils/fork-tree/Cargo.toml

@@ -10,4 +10,4 @@ description = "Utility library for managing tree-like ordered data with logic fo
 documentation = "https://docs.rs/fork-tree"
 
 [dependencies]
-codec = { package = "parity-scale-codec", version = "1.0.0", features = ["derive"] }
+codec = { package = "parity-scale-codec", version = "1.2.0", features = ["derive"] }