t: use test_might_fail for diff and grep

diff --git a/t/t5709-clone-refspec.sh b/t/t5709-clone-refspec.sh
index 6f1ea984d45eb931179dce751be9f7b8bc70265a..7ace2535c80e988e353ae09ecbf3bb24d6106ecc 100755 (executable)
--- a/t/t5709-clone-refspec.sh
+++ b/t/t5709-clone-refspec.sh
@@ -147,7 +147,7 @@ test_expect_success '--single-branch with detached' '
                git for-each-ref refs/remotes/origin |
                sed -e "/HEAD$/d" \
                    -e "s|/remotes/origin/|/heads/|" >../actual
-       )
+       ) &&
        # nothing
        >expect &&
        test_cmp expect actual