test: adjust library tests for PHPunit deprecations

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

tests/lib/App/AppManagerTest.php

@@ -159,15 +159,15 @@ class AppManagerTest extends TestCase {
 		}
 	}
 
-	public function dataGetAppIcon(): array {
+	public static function dataGetAppIcon(): array {
 		$nothing = function ($appId) {
-			$this->assertEquals('test', $appId);
+			self::assertEquals('test', $appId);
 			throw new \RuntimeException();
 		};
 
 		$createCallback = function ($workingIcons) {
 			return function ($appId, $icon) use ($workingIcons) {
-				$this->assertEquals('test', $appId);
+				self::assertEquals('test', $appId);
 				if (in_array($icon, $workingIcons)) {
 					return '/path/' . $icon;
 				}

tests/lib/Files/FilenameValidatorTest.php

@@ -409,7 +409,7 @@ class FilenameValidatorTest extends TestCase {
 		$this->assertEquals($expected, $validator->sanitizeFilename($filename));
 	}
 
-	public function dataSanitizeFilename(): array {
+	public static function dataSanitizeFilename(): array {
 		return [
 			'valid name' => [
 				'a * b.txt', ['.htaccess'], [], [], [], 'a * b.txt'