chore(security): optimize cargo-audit workflow

.github/workflows/audit.yml

@@ -1,12 +1,23 @@
 name: Security Audit
+
 on:
   schedule:
-    - cron: '0 0 * * 0'
+    - cron: "0 0 * * 0"
+
 jobs:
   audit:
-    runs-on: ubuntu-latest
+    name: Audit
+    runs-on: ubuntu-20.04
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions-rs/audit-check@v1
+      - name: Checkout the repository
+        uses: actions/checkout@master
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          profile: minimal
+          override: true
+      - name: Run cargo-audit
+        uses: actions-rs/audit-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}