fixup! status: offer *not* to lock the index and update it

This re-adds the regression test that would have found the issue before
releasing v2.15.0 *grrrr*.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/t7508-status.sh

@@ -1671,6 +1671,17 @@ test_expect_success '"Initial commit" should not be noted in commit template' '
 	test_i18ngrep ! "Initial commit" output
 '
 
+test_expect_success '--no-lock-index prevents index update and is deprecated' '
+	test-chmtime =1234567890 .git/index &&
+	git status --no-lock-index 2>err &&
+	grep "no-lock-index is deprecated" err &&
+	test-chmtime -v +0 .git/index >out &&
+	grep ^1234567890 out &&
+	git status &&
+	test-chmtime -v +0 .git/index >out &&
+	! grep ^1234567890 out
+'
+
 test_expect_success '--no-optional-locks prevents index update' '
 	test-chmtime =1234567890 .git/index &&
 	git --no-optional-locks status &&