Update Rust crate heapless to 0.8

Author: renovate[bot]

Cargo.toml

@@ -9,7 +9,7 @@ repository = "https://github.com/arkedge/eb90-rs"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-heapless = "0.7"
+heapless = "0.8"
 crc = "2"
 tokio-util = { version = "0.7", features = ["codec"], optional = true }
 bytes = { version = "1.4.0", optional = true }