Update heapless to v0.8

Cargo.toml

@@ -24,7 +24,7 @@ libc = { version = "0.2.18", optional = true }
 bitflags = { version = "1.0", default-features = false }
 defmt = { version = "0.3", optional = true }
 cfg-if = "1.0.0"
-heapless = "0.7.15"
+heapless = "0.8"
 
 [dev-dependencies]
 env_logger = "0.10"
@@ -37,7 +37,7 @@ rstest = "0.17"
 std = ["managed/std", "alloc"]
 alloc = ["managed/alloc", "defmt?/alloc"]
 verbose = []
-defmt = [ "dep:defmt", "heapless/defmt", "heapless/defmt-impl" ]
+defmt = [ "dep:defmt", "heapless/defmt-03" ]
 "medium-ethernet" = ["socket"]
 "medium-ip" = ["socket"]
 "medium-ieee802154" = ["socket", "proto-sixlowpan"]