Update GitHub actions to work in Taskwarrior

This moves the workspace Cargo.toml to the root of the repository, so
that the "actions-rs/cargo" action can find it.

rust/.github/workflows/audit.yml

@@ -1,19 +0,0 @@
-name: Security
-
-on:
-  schedule:
-    - cron: '0 0 * * *'
-  push:
-    paths:
-      - '**/Cargo.toml'
-      - '**/Cargo.lock'
-
-jobs:
-  audit:
-    runs-on: ubuntu-latest
-    name: "Audit Dependencies"
-    steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/audit-check@v1
-        with:
-          token: ${{ secrets.GITHUB_TOKEN }}