ci(build): always use latest toolchain

.github/workflows/build.yml

@@ -16,6 +16,11 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+
       - name: Install build deps
         run: sudo apt install libgtk-3-dev libgtk-layer-shell-dev