test: Remove suffix to reduce warnings about not extending TestCase

Signed-off-by: Joas Schilling <coding@schilljs.com>

tests/phpunit-autotest-external.xml

@@ -10,7 +10,7 @@
 		 timeoutForLargeTests="900"
 >
 	<testsuite name='ownCloud files external'>
-		<directory suffix=".php">../apps/files_external/tests</directory>
+		<directory>../apps/files_external/tests</directory>
 		<!-- exclude backends as they are called separately -->
 		<exclude>../apps/files_external/tests/Storage/</exclude>
 	</testsuite>

tests/phpunit-autotest.xml

@@ -14,8 +14,8 @@
 		 convertDeprecationsToExceptions="true"
 		 xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.6/phpunit.xsd">
 	<testsuite name="Nextcloud Server">
-		<directory suffix=".php">lib/</directory>
-		<directory suffix=".php">Core/</directory>
+		<directory>lib/</directory>
+		<directory>Core/</directory>
 		<file>apps.php</file>
 	</testsuite>
 	<coverage>