Ignore RUSTSEC-2020-0071 in audit.

It is about some old version of the time crate used by chrono,
but the chrono authors say that they don't actually use the
affected functions.

See chronotope/chrono#602 (comment)

.github/workflows/cargo-audit.yml

@@ -3,7 +3,7 @@ on:
   push:
     paths:
       # Run if workflow changes
-      - '.github/workflows/audit.yml'
+      - '.github/workflows/cargo-audit.yml'
       # Run on changed dependencies
       - '**/Cargo.toml'
       - '**/Cargo.lock'
@@ -25,4 +25,6 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: actions-rust-lang/audit@v1
-        name: Audit Rust Dependencies
+        name: Audit Rust Dependencies
+        with:
+          ignore: RUSTSEC-2020-0071