Scope candidate blob readers to validation

internal/validation/tree_test.go

@@ -38,6 +38,7 @@ func TestReadCandidateTreeUsesCapturedCommitAndEnumeratesGitEntries(t *testing.T
 	if err != nil {
 		t.Fatalf("ReadCandidateTree() error = %v", err)
 	}
+	cleanupCandidateTree(t, tree)
 	entries := make(map[string]gitTreeEntry, len(tree.Entries()))
 	for _, entry := range tree.Entries() {
 		entries[entry.Path] = gitTreeEntry{mode: entry.Mode, kind: entry.Type, size: entry.Size, hasSize: entry.HasSize}
@@ -77,6 +78,11 @@ func TestReadCandidateTreeUsesCapturedCommitAndEnumeratesGitEntries(t *testing.T
 	}
 }
 
+func cleanupCandidateTree(tb testing.TB, tree *CandidateTree) {
+	tb.Helper()
+	tb.Cleanup(func() { _ = tree.Close() })
+}
+
 func TestReadCandidateTreePreservesGitProcessError(t *testing.T) {
 	repository := newTreeRepository(t)
 	_, err := ReadCandidateTree(context.Background(), repository, strings.Repeat("f", 40))