Update system-deps requirement from 6.2 to 7.0

Updates the requirements on [system-deps](https://github.com/gdesmott/system-deps) to permit the latest version.
- [Release notes](https://github.com/gdesmott/system-deps/releases)
- [Changelog](https://github.com/gdesmott/system-deps/blob/main/CHANGELOG.md)
- [Commits](https://github.com/gdesmott/system-deps/compare/system-deps@6.2.0...v7.0.0)

---
updated-dependencies:
- dependency-name: system-deps
  dependency-type: direct:production
...

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

dav1d-sys/Cargo.toml

@@ -11,7 +11,7 @@ readme = "../README.md"
 build = "build.rs"
 
 [build-dependencies]
-system-deps = "6.2"
+system-deps = "7.0"
 
 [dependencies]
 libc = "0.2"