t7406: correct test case for submodule-update initial population

There are three issues with the test:

* The syntax of the here-doc was wrong, such that the entire test was
  sucked into the here-doc, which is why the test succeeded.

* The variable $submodulesha1 was not expanded as it was inside a quoted
  here text.  We do not want to quote EOF marker for this.

* The redirection from the git command to the output file for comparison
  was wrong as the -C operator from git doesn't apply to the redirect path.
  Also we're interested in stderr of that command.

Noticed-by: Jan Palus <jan.palus@gmail.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: gitster

t/t7406-submodule-update.sh

@@ -425,11 +425,11 @@ test_expect_success 'submodule update - command in .git/config catches failure -
 '
 
 test_expect_success 'submodule update - command run for initial population of submodule' '
-	cat <<-\ EOF >expect
+	cat >expect <<-EOF &&
 	Execution of '\''false $submodulesha1'\'' failed in submodule path '\''submodule'\''
-	EOF &&
+	EOF
 	rm -rf super/submodule &&
-	test_must_fail git -C super submodule update >../actual &&
+	test_must_fail git -C super submodule update 2>actual &&
 	test_cmp expect actual &&
 	git -C super submodule update --checkout
 '