github: Fix CI workflow.

.github/workflows/ci.yml

@@ -32,7 +32,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-        uses: actions-rs/toolchain@v1
+      - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
           override: true