t9001: Fix test prerequisites

Add in missing Perl prerequisites for new tests of send-email.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9001-send-email.sh

@@ -1035,7 +1035,7 @@ test_expect_success $PREREQ '--8bit-encoding also treats subject' '
 # Note that the patches in this test are deliberately out of order; we
 # want to make sure it works even if the cover-letter is not in the
 # first mail.
-test_expect_success 'refusing to send cover letter template' '
+test_expect_success $PREREQ 'refusing to send cover letter template' '
 	clean_fake_sendmail &&
 	rm -fr outdir &&
 	git format-patch --cover-letter -2 -o outdir &&
@@ -1051,7 +1051,7 @@ test_expect_success 'refusing to send cover letter template' '
 	test -z "$(ls msgtxt*)"
 '
 
-test_expect_success '--force sends cover letter template anyway' '
+test_expect_success $PREREQ '--force sends cover letter template anyway' '
 	clean_fake_sendmail &&
 	rm -fr outdir &&
 	git format-patch --cover-letter -2 -o outdir &&