Allow cargo-audit workflow to fail (bytecodealliance#8280)

Currently this workflow fails about 50% of the time due to what appears
to be rate limiting issues. I'm personally receiving emails every time
this fails and would rather not continue to receive emails. I've updated
this to allow failure to hopefully stop notifying me about this.

.github/workflows/cargo-audit.yml

@@ -13,3 +13,6 @@ jobs:
       - uses: rustsec/audit-check@v1.4.1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
+        # This seems to hit rate limits about 50% of the time, unclear why, but
+        # emailing us once every few days is not the most useful thing.
+        continue-on-error: true