[PHPUnit] Add migration for 7.5 assertStringContainsString

[Slamdunk]

Reference: https://github.com/sebastianbergmann/phpunit/blob/7.5.0/ChangeLog-7.5.md

Implemented sebastianbergmann/phpunit#3422: Added assertStringContainsString(), assertStringContainsStringIgnoringCase(), assertStringNotContainsString(), and assertStringNotContainsStringIgnoringCase()

Using the methods assertContains() and assertNotContains() on string haystacks is now deprecated. There is no behavioral change in this version of PHPUnit. Using these methods on string haystacks will trigger a deprecation warning in PHPUnit 8 and in PHPUnit 9 these methods cannot be used on on string haystacks anymore.

The optional parameters $ignoreCase, $checkForObjectIdentity, and $checkForNonObjectIdentity of assertContains() and assertNotContains() are now deprecated. There is no behavioral change in this version of PHPUnit. Using these parameters will trigger a deprecation warning in PHPUnit 8 and in PHPUnit 9 these parameters will be removed.