build(deps): update which requirement from 4 to 6

Updates the requirements on [which](https://github.com/harryfei/which-rs) to permit the latest version.
- [Release notes](https://github.com/harryfei/which-rs/releases)
- [Changelog](https://github.com/harryfei/which-rs/blob/master/CHANGELOG.md)
- [Commits](harryfei/which-rs@4.0.0...6.0.0)

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

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

ndk-build/Cargo.toml

@@ -17,4 +17,4 @@ dunce = "1"
 quick-xml = { version = "0.26", features = ["serialize"] }
 serde = { version = "1", features = ["derive"] }
 thiserror = "1"
-which = "4"
+which = "6"