Update heapless requirement from 0.8.0 to 0.9.0

Updates the requirements on [heapless](https://github.com/rust-embedded/heapless) to permit the latest version.
- [Release notes](https://github.com/rust-embedded/heapless/releases)
- [Changelog](https://github.com/rust-embedded/heapless/blob/main/CHANGELOG.md)
- [Commits](rust-embedded/heapless@v0.8.0...v0.9.0)

---
updated-dependencies:
- dependency-name: heapless
  dependency-version: 0.9.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Cargo.toml

@@ -11,4 +11,4 @@ readme = "README.md"
 exclude = [".github"]
 
 [dependencies]
-heapless = "0.8.0"
+heapless = "0.9.0"