t5310: disable GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP

Generating a MIDX bitmap confuses many of the tests in t5310, which
expect to control whether and how bitmaps are written. Since the
relevant MIDX-bitmap tests here are covered already in t5326, let's just
disable the flag for the whole t5310 script.

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

t/t5310-pack-bitmaps.sh

@@ -8,6 +8,10 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 . "$TEST_DIRECTORY"/lib-bundle.sh
 . "$TEST_DIRECTORY"/lib-bitmap.sh
 
+# t5310 deals only with single-pack bitmaps, so don't write MIDX bitmaps in
+# their place.
+GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP=0
+
 objpath () {
 	echo ".git/objects/$(echo "$1" | sed -e 's|\(..\)|\1/|')"
 }