Update assert_hex requirement from 0.2 to 0.4

Updates the requirements on [assert_hex](https://github.com/wcampbell0x2a/assert_hex) to permit the latest version.
- [Release notes](https://github.com/wcampbell0x2a/assert_hex/releases)
- [Changelog](https://github.com/wcampbell0x2a/assert_hex/blob/master/CHANGELOG.md)
- [Commits](wcampbell0x2a/assert_hex@v0.2.0...v0.4.0)

---
updated-dependencies:
- dependency-name: assert_hex
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Cargo.toml

@@ -21,4 +21,4 @@ defmt = { version = "0.3", optional = true }
 defmt-impl = ["defmt", "heapless/defmt-impl"]
 
 [dev-dependencies]
-assert_hex = "0.2"
+assert_hex = "0.4"