Add test file for rust-src-dir input

Author: jonasbb

.github/workflows/ci-sub.yaml

@@ -0,0 +1,20 @@
+name: "Test Suite"
+on:
+  push:
+  pull_request:
+
+jobs:
+  formatting:
+    name: cargo fmt
+    runs-on: ubuntu-latest
+    steps:
+      - run: rustup self uninstall
+      - uses: actions/checkout@v5
+      - uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          toolchain: stable
+          components: clippy
+          rust-src-dir: proj
+          override: false
+      - uses: Swatinem/rust-cache@v2
+      - run: cargo clippy --all-targets --all-features --locked -- -D