t6300: drop newline from wrapped test title

We don't usually include newlines in test titles, because you get funny
TAP output like:

  ok 417 - show good signature with custom format
  ok 418 - show good signature with custom format
  			    with ssh
  ok 419 - signature atom with grade option and bad signature

where a TAP parser would ignore the extra line anyway, giving the wrong
title. This comes from 26c9c03 (ref-filter: add new "signature" atom,
2023-06-04), and I think it was probably just editor line wrapping.

I checked for other cases with:

  git grep "test_expect_success [A-Z_,]* '[^']*$"
  git grep 'test_expect_success [A-Z_,]* "[^"]*$'

but this was the only hit.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

t/t6300-for-each-ref.sh

@@ -2003,8 +2003,7 @@ test_expect_success GPG 'show good signature with custom format' '
 		--format="$GRADE_FORMAT" >actual &&
 	test_cmp expect actual
 '
-test_expect_success GPGSSH 'show good signature with custom format
-			    with ssh' '
+test_expect_success GPGSSH 'show good signature with custom format with ssh' '
 	test_config gpg.ssh.allowedSignersFile "${GPGSSH_ALLOWED_SIGNERS}" &&
 	FINGERPRINT=$(ssh-keygen -lf "${GPGSSH_KEY_PRIMARY}" | awk "{print \$2;}") &&
 	cat >expect.tmpl <<-\EOF &&