build: Bump x86_64 from 0.15.3 to 0.15.4

Bumps [x86_64](https://github.com/rust-osdev/x86_64) from 0.15.3 to 0.15.4.
- [Changelog](https://github.com/rust-osdev/x86_64/blob/master/Changelog.md)
- [Commits](rust-osdev/x86_64@v0.15.3...v0.15.4)

---
updated-dependencies:
- dependency-name: x86_64
  dependency-version: 0.15.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

Cargo.lock

@@ -40,7 +40,7 @@ chrono = { version = "0.4", default-features = false }
 
 [target.'cfg(target_arch = "x86_64")'.dependencies]
 uart_16550 = "0.4.0"
-x86_64 = { version = "0.15.3", default-features = false, features = [
+x86_64 = { version = "0.15.4", default-features = false, features = [
     "instructions",
 ] }