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
```

phpunit.xml

@@ -8,7 +8,7 @@
 	convertWarningsToExceptions="true"
 	>
 	<testsuites>
-		<testsuite>
+		<testsuite name="view-all-posts-pages">
 			<directory prefix="test-" suffix=".php">./tests/</directory>
 			<exclude>./tests/test-sample.php</exclude>
 		</testsuite>