feat: checkout fumi as a sibling dir in CI to match the local path dependency

.forgejo/workflows/macos.yml

@@ -11,6 +11,15 @@ jobs:
     runs-on: macos-arm64
     steps:
       - uses: https://code.forgejo.org/actions/checkout@v4
+        with:
+          path: carrier
+      # Cargo.toml depends on fumi-core via a relative sibling path
+      # (../fumi/core), matching how it's checked out locally. Fetched as
+      # its own sibling checkout here so that path resolves the same way.
+      - uses: https://code.forgejo.org/actions/checkout@v4
+        with:
+          repository: randogoth/fumi
+          path: fumi
       # Forgejo auto-injects GITHUB_TOKEN (GH Actions compatibility), scoped
       # to this Forgejo instance. Nix auto-detects that env var and assumes
       # it's a github.com credential, so it sends it to api.github.com when
@@ -18,5 +27,6 @@ jobs:
       # Clearing it here falls back to unauthenticated (fine for public
       # nixpkgs fetches, same as this succeeds locally with no token set).
       - run: devbox run check
+        working-directory: carrier
         env:
           GITHUB_TOKEN: ""