allow unicode license (#5337)

# Objective

- Crate `unicode-ident` added the [unicode license](https://github.com/dtolnay/unicode-ident/blob/master/LICENSE-UNICODE). See https://github.com/dtolnay/unicode-ident#license. The only requirement seems to be to include the license in the distribution
- This makes license check fail

## Solution

- The license should be ok for Bevy, add it to the allowed licenses

deny.toml

@@ -23,6 +23,9 @@ allow = [
     "BSD-2-Clause",
     "CC0-1.0",
 ]
+exceptions = [
+    { name = "unicode-ident", allow = ["Unicode-DFS-2016"] },
+]
 default = "deny"
 
 [bans]