ci: Don't use actions-rs actions (#498)

These haven't been maintained in some time, so just do the
steps directly as other jobs do.

.github/workflows/ci.yml

@@ -8,10 +8,8 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: actions-rs/toolchain@v1
-        with:
-          toolchain: stable
-          components: rustfmt, clippy
+      - run: rustup update --no-self-update stable
+      - run: rustup default stable
 
       # make sure all code has been formatted with rustfmt and linted with clippy
       - name: rustfmt