t: fix trivial &&-chain breakage

These are tests which are missing a link in their &&-chain,
but during a setup phase. We may fail to notice failure in
commands that build the test environment, but these are
typically not expected to fail at all (but it's still good
to double-check that our test environment is what we
expect).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index 256affc..c39e500 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -802,7 +802,7 @@
 '
 
 test_expect_success '--signature-file overrides format.signaturefile' '
-	cat >other-mail-signature <<-\EOF
+	cat >other-mail-signature <<-\EOF &&
 	Use this other signature instead of mail-signature.
 	EOF
 	test_config format.signaturefile mail-signature &&