Ignore derivative in Cargo deny (#3708)

`derivative` is marked as unmaintained by RUSTSEC but still used in
Charon. We exclude it from the deny check until `derivative` is replaced
in Charon (AeneasVerif/charon#459).

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under the terms of the Apache 2.0 and MIT licenses.

deny.toml

@@ -1,6 +1,12 @@
 # Copyright Kani Contributors
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
+[graph]
+# derivative is marked as unmaintained by RUSTSEC but still used in
+# Charon. We exclude it from the deny check until derivative is replaced
+# from Charon (https://github.com/AeneasVerif/charon/pull/459).
+exclude = ["derivative"]
+
 # This section is considered when running `cargo deny check advisories`
 # More documentation for the advisories section can be found here:
 # https://embarkstudios.github.io/cargo-deny/checks/advisories/cfg.html