Fix CI: use the rust-ci runner instead of overriding the docker-labeled runner's container

The docker-labeled runner's image is node:20-bookworm, needed for the
checkout/cache actions (both Node-based). Overriding it with
container: rust:1-bookworm dropped Node from the image entirely, so
checkout failed with "node: executable file not found in $PATH". The
rust-ci label (see sporah's workflow) points at a custom image with
both Rust and Node preinstalled, avoiding the conflict.

.forgejo/workflows/ci.yml

@@ -6,15 +6,12 @@ on:
 
 jobs:
   test:
-    runs-on: docker
-    container: rust:1-bookworm
-
+    runs-on: rust-ci
     steps:
-      - name: Checkout
-        uses: https://code.forgejo.org/actions/checkout@v4
+      - uses: actions/checkout@v4
 
       - name: Cache cargo registry and build artifacts
-        uses: https://code.forgejo.org/actions/cache@v4
+        uses: actions/cache@v4
         with:
           path: |
             ~/.cargo/registry
@@ -24,9 +21,6 @@ jobs:
           restore-keys: |
             cargo-${{ runner.os }}-
 
-      - name: Install rustfmt and clippy
-        run: rustup component add rustfmt clippy
-
       - name: Check formatting
         run: cargo fmt -- --check