Ignore RUSTSEC-2023-0089 until postcard is updated (#19038)

# Objective

- CI fails due to `atomic-polyfill` being unmaintained

## Solution

- Dependency chain of `postcard -> heapless -> atomic-polyfill` .
`heapless` is updated. `postcard` has not yet.
- See jamesmunns/postcard#223
- Ignore the advisory for now

## Testing

- CI with this PR

---------

Co-authored-by: MichiRecRoom <1008889+LikeLakers2@users.noreply.github.com>

Author: Zeophlite

deny.toml

@@ -8,6 +8,9 @@ ignore = [
   # See: https://rustsec.org/advisories/RUSTSEC-2024-0436
   # Bevy relies on this in multiple indirect ways, so ignoring it is the only feasible current solution
   "RUSTSEC-2024-0436",
+  # unmaintained: postcard -> heapless -> atomic-polyfill
+  # See https://github.com/jamesmunns/postcard/issues/223
+  "RUSTSEC-2023-0089",
 ]
 
 [licenses]