t1308: relax the test verifying that empty alias values are disallowed

We are about to change the way aliases are expanded, to use the early
config machinery.

This machinery reports errors in a slightly different manner than the
cached config machinery.

Let's not get hung up by the precise wording of the message mentioning
the line number. It is really sufficient to verify that all the relevant
information is given to the user.
Signed-off-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t1308-config-set.sh

@@ -215,7 +215,9 @@ test_expect_success 'check line errors for malformed values' '
 		br
 	EOF
 	test_expect_code 128 git br 2>result &&
-	test_i18ngrep "fatal: .*alias\.br.*\.git/config.*line 2" result
+	test_i18ngrep "missing value for .alias\.br" result &&
+	test_i18ngrep "fatal: .*\.git/config" result &&
+	test_i18ngrep "fatal: .*line 2" result
 '
 
 test_expect_success 'error on modifying repo config without repo' '