t9300: use test_cmp_bin instead of test_cmp to compare binary files

test_cmp is intended to produce diff output for human consumption. The
input in one instance in t9300-fast-import.sh are binary files, however.
Use test_cmp_bin to compare the files.

This was noticed because on Windows we have a special implementation of
test_cmp in pure bash code (to ignore differences due to intermittent CR
in actual output), and bash runs into an infinite loop due to the binary
nature of the input.
Signed-off-by: NJohannes Sixt <j6t@kdbg.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t9300-fast-import.sh

@@ -2687,7 +2687,7 @@ test_expect_success 'R: verify created pack' '
 test_expect_success \
 	'R: verify written objects' \
 	'git --git-dir=R/.git cat-file blob big-file:big1 >actual &&
-	 test_cmp expect actual &&
+	 test_cmp_bin expect actual &&
 	 a=$(git --git-dir=R/.git rev-parse big-file:big1) &&
 	 b=$(git --git-dir=R/.git rev-parse big-file:big2) &&
 	 test $a = $b'