test: use correct matrix syntax

.forgejo/workflows/test.yml

@@ -5,20 +5,26 @@ on:
 jobs:
   test:
     runs-on: docker
+    strategy:
+      matrix:
+        toolchain:
+          - name: stable
+          - name: nightly
+
     steps:
       - uses: actions/checkout@v4
 
       - name: Test
         uses: https://git.kemitix.net/kemitix/rust@next
         with:
-          args: cargo test
+          args: ${{ matrix.toolchain.name }} cargo test
 
       - name: Build
         uses: https://git.kemitix.net/kemitix/rust@next
         with:
-          args: cargo build
+          args: ${{ matrix.toolchain.name }} cargo build
 
       - name: Run
         uses: https://git.kemitix.net/kemitix/rust@next
         with:
-          args: cargo run
+          args: ${{ matrix.toolchain.name }} cargo run