cargo: bump cc in /src/exercises/bare-metal/rtc in the patch group

Bumps the patch group in /src/exercises/bare-metal/rtc with 1 update: [cc](https://github.com/rust-lang/cc-rs).


Updates `cc` from 1.1.14 to 1.1.15
- [Release notes](https://github.com/rust-lang/cc-rs/releases)
- [Changelog](https://github.com/rust-lang/cc-rs/blob/main/CHANGELOG.md)
- [Commits](rust-lang/cc-rs@cc-v1.1.14...cc-v1.1.15)

---
updated-dependencies:
- dependency-name: cc
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: patch
...

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

src/exercises/bare-metal/rtc/Cargo.toml

@@ -15,4 +15,4 @@ smccc = "0.1.1"
 spin = "0.9.8"
 
 [build-dependencies]
-cc = "1.1.14"
+cc = "1.1.15"