Materialize LFS objects with an explicit git lfs checkout

Problem

On persistent/self-hosted runners that reuse a working directory across jobs, LFS-tracked files can be left as pointer files instead of real content when a lfs: false checkout precedes a lfs: true checkout of the same repo.

Sequence that triggers it:
 1. A lfs: false run sets GIT_LFS_SKIP_SMUDGE=1, so git checkout writes LFS files to the working tree as pointers.
 2. A later lfs: true run on the same worktree fetches the objects into .git/lfs, but git checkout sees the tree already at the target commit and does not re-smudge the already-present pointer files.

Result: the objects are in the local cache, but the working tree still contains pointers. The action relies on the smudge filter firing during git checkout to materialize content — which holds on a clean tree (GitHub-hosted runners) but not on a reused one.

Related: actions/checkout#270

.github/workflows/test.yml

@@ -136,6 +136,16 @@ jobs:
         run: __test__/verify-sparse-checkout-non-cone-mode.sh
 
       # LFS
+      # First check out without LFS so the reused worktree is left holding LFS
+      # pointer files; the `lfs: true` checkout below must then materialize them
+      # rather than leave the stale pointers in place (#270).
+      - name: Checkout LFS pointers (reused worktree setup)
+        uses: ./
+        with:
+          repository: actions/checkout # hardcoded, otherwise doesn't work from a fork
+          ref: test-data/v2/lfs
+          path: lfs
+          lfs: false
       - name: Checkout LFS
         uses: ./
         with: