[php8-compat][phpunit8][NFC] Fix PHPUnit Warnings and fix a php error on f…

[seamuslee001]

…unction declaration syntax in core extension tests

Overview

This fixes a few phpunit8 warnings generated

# Warning Using assertContains() with string haystacks is deprecated and will not be supported in PHPUnit 9. Refactor your test to use assertStringContainsString() or assertStringContainsStringIgnoringCase() instead.

This also fixes an error

Fatal error: Declaration of Civi\AfformMock\FormTestCase::setUp() must be compatible with PHPUnit\Framework\TestCase::setUp(): void in /home/jenkins/bknix-edge/build/build-0/web/sites/all/modules/civicrm/ext/afform/mock/tests/phpunit/Civi/AfformMock/FormTestCase.php on line 32

Before

Warnings issued in phpunit8 and fatal error triggered

After

No warnings and no fatal error

ping @eileenmcnaughton @totten @demeritcowboy @colemanw

[seamuslee001]

Jenkins test this please

[civibot]

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