Upgrade toolchain

Newest rustc contains an important bugfix to AVR's code generator
(rust-lang/rust#98567).

Ref: Rahix/avr-hal-template#9

Author: Rahix

rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
-channel = "nightly-2022-06-13"
+channel = "nightly-2022-07-10"
 components = [ "rust-src" ]
 profile = "minimal"