[NFC] Fix Membership Type Test error on php7.4

[seamuslee001]

Overview

This fixes a test failure on the MembershipType Test suite on PHP 7.4 caused by trying to do array access on value of type int

Before

Test fails on PHP 7.4

<error type="PHPUnit\Framework\Error\Notice">api_v3_MembershipTypeTest::testEnableMembershipTypeOnContributionPage
Trying to access array offset on value of type int

**/home/jenkins/bknix-edge/build/build-2/web/sites/all/modules/civicrm/tests/phpunit/api/v3/MembershipTypeTest.php:326**

After

Test passes

ping @eileenmcnaughton

[civibot]

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