t/t5319-multi-pack-index.sh: drop early 'test_done'

In 6ce9d55 (midx-write: skip rewriting MIDX with `--stdin-packs`
unless needed, 2025-12-10), an extra 'test_done' was added, causing the
test script to finish before having run all of its tests.

Dropping this extraneous 'test_done' exposes a bug from commit
6ce9d55 that causes a subsequent test to fail. Mark that test with a
'test_expect_failure' for now, and the subsequent commit will explain
and fix the bug.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ttaylorr

t/t5319-multi-pack-index.sh

@@ -415,8 +415,6 @@ test_expect_success 'up-to-date multi-pack-index is retained' '
 	)
 '
 
-test_done
-
 test_expect_success 'verify multi-pack-index success' '
 	git multi-pack-index verify --object-dir=$objdir
 '
@@ -565,7 +563,7 @@ test_expect_success 'git fsck suppresses MIDX output with --no-progress' '
 	! grep "Verifying object offsets" err
 '
 
-test_expect_success 'corrupt MIDX is not reused' '
+test_expect_failure 'corrupt MIDX is not reused' '
 	corrupt_midx_and_verify $MIDX_BYTE_OFFSET "\377" $objdir \
 		"incorrect object offset" &&
 	git multi-pack-index write 2>err &&