ci: Check formatting

Also moves rustup installation to a seperate workflow and
enables caching.
The sccache action required a github.com api token, so we set
all that up too.

.forgejo/workflows/formatting.yml

@@ -0,0 +1,44 @@
+name: Rust Formatting
+
+on:
+    push:
+    pull_request:
+
+jobs:
+  format:
+    name: Format
+    runs-on: ubuntu-latest
+    env:
+      SCCACHE_GHA_ENABLED: "true"
+      RUSTC_WRAPPER: "sccache"
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      
+      - name: Install rust
+        uses: ./.forgejo/actions/rust-toolchain
+        with:
+          toolchain: "nightly"
+          components: "rustfmt"
+
+      - uses: https://github.com/actions/create-github-app-token@v2
+        id: app-token
+        with:
+          app-id: ${{ vars.GH_APP_ID }}
+          private-key: ${{ secrets.GH_APP_PRIVATE_KEY }}
+          github-api-url: https://api.github.com
+          owner: ${{ vars.GH_APP_OWNER }}
+          repositories: ""
+      - name: Install sccache
+        uses: ./.forgejo/actions/sccache
+        with:
+          token: ${{ steps.app-token.outputs.token }}
+      - name: Check formatting
+        run: |
+          cargo +nightly fmt --all -- --check
+
+      - name: Show sccache stats
+        run: sccache --show-stats

.forgejo/workflows/release-image.yml

@@ -79,16 +79,13 @@ jobs:
         run: echo '${{ toJSON(fromJSON(needs.define-variables.outputs.build_matrix)) }}'
       - name: Echo matrix
         run: echo '${{ toJSON(matrix) }}'
-      - run: |
-          if ! command -v rustup &> /dev/null ; then
-            curl --proto '=https' --tlsv1.2 --retry 10 --retry-connrefused -fsSL "https://sh.rustup.rs" | sh -s -- --default-toolchain none -y
-            echo "${CARGO_HOME:-$HOME/.cargo}/bin" >> $GITHUB_PATH
-          fi
       
       - name: Checkout repository
         uses: actions/checkout@v4
         with:
           persist-credentials: false
+      - name: Install rust
+        uses: ./.forgejo/actions/rust-toolchain
 
       - name: Cache timelord-cli installation
         id: cache-timelord-bin