Use dtolnay/rust-toolchain's miri toolchain

This defaults to components miri + rust-src.

Author: dtolnay

.github/workflows/ci.yml

@@ -62,9 +62,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: dtolnay/rust-toolchain@nightly
-        with:
-          components: miri, rust-src
+      - uses: dtolnay/rust-toolchain@miri
       - run: cargo miri test
         env:
           MIRIFLAGS: -Zmiri-strict-provenance