Fix fatal in test run under PHP 8

Fatal error: Declaration of PostFilters::setUp() must be compatible with Yoast\PHPUnitPolyfills\TestCases\TestCase::setUp(): void in /builds/wp-plugins/view-all-posts-pages/tests/test-post-filters.php on line 40

tests/bootstrap.php

@@ -27,5 +27,8 @@ function _manually_load_plugin() {
 }
 tests_add_filter( 'muplugins_loaded', '_manually_load_plugin' );
 
+// Load base class for compatibility.
+require __DIR__ . '/class-test-case.php';
+
 // Start up the WP testing environment.
 require $_tests_dir . '/includes/bootstrap.php';