Add constant_time_eq to license exception list of tidy tool

Author: flip1995

src/tools/tidy/src/deps.rs

@@ -45,6 +45,7 @@ const EXCEPTIONS: &[&str] = &[
     "im-rc",              // MPL-2.0+, cargo
     "adler32",            // BSD-3-Clause AND Zlib, cargo dep that isn't used
     "fortanix-sgx-abi",   // MPL-2.0+, libstd but only for `sgx` target
+    "constant_time_eq",   // CC0-1.0, rustfmt
 ];
 
 /// Which crates to check against the whitelist?