Stop ignoring RUSTSEC-2020-0168 in the testframework audit CI job

Author: faern

.github/workflows/cargo-audit.yml

@@ -33,5 +33,4 @@ jobs:
           # Ignored audit issues. This list should be kept short, and effort should be
           # put into removing items from the list.
           # RUSTSEC-2023-0057,RUSTSEC-2023-0058 - Unsoundness in `inventory`.
-          # RUSTSEC-2020-0168 - `mach` is unmaintained. Can be fixed by upgrading `serialport`.
-          ignore: RUSTSEC-2023-0057,RUSTSEC-2023-0058,RUSTSEC-2020-0168
+          ignore: RUSTSEC-2023-0057,RUSTSEC-2023-0058