t6300: fix issues related to %(contents:size)

b6839fda68 (ref-filter: add support for %(contents:size), 2020-07-16)
added a new format for ref-filter, and added a function to generate
tests for this new feature in t6300.  Unfortunately, it tries to run
`test_expect_sucess' instead of `test_expect_success', and writes
$expect to `expected', but tries to read `expect'.  Those two issues
were probably unnoticed because the script only printed errors, but did
not crash.  This fixes these issues.

Signed-off-by: Alban Gruin <alban.gruin@gmail.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6300-for-each-ref.sh

@@ -66,9 +66,9 @@ test_atom() {
 		esac
 		# Leave $expect unquoted to lose possible leading whitespaces
 		echo $expect >expected
-		test_expect_${4:-sucess} $PREREQ "basic atom: $1 contents:size" '
+		test_expect_${4:-success} $PREREQ "basic atom: $1 contents:size" '
 			git for-each-ref --format="%(contents:size)" "$ref" >actual &&
-			test_cmp expect actual
+			test_cmp expected actual
 		'
 	fi
 }