chore(deps): Update tough requirement from 0.14 to 0.15

Updates the requirements on [tough](https://github.com/awslabs/tough) to permit the latest version.
- [Release notes](https://github.com/awslabs/tough/releases)
- [Commits](awslabs/tough@tough-v0.14.0...tough-v0.15.0)

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

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

Cargo.toml

@@ -115,7 +115,7 @@ sha2 = { version = "0.10.6", features = ["oid"] }
 signature = { version = "2.0" }
 thiserror = "1.0.30"
 tokio = { version = "1.17.0", features = ["rt"] }
-tough = { version = "0.14", features = ["http"], optional = true }
+tough = { version = "0.15", features = ["http"], optional = true }
 tracing = "0.1.31"
 url = "2.2.2"
 x509-cert = { version = "0.2.2", features = ["pem", "std"] }