fix: incompatible overwrite for AppConfig

Signed-off-by: Anna Larch <anna@nextcloud.com>

Author: miaulalala

lib/AppConfigOverwrite.php

@@ -19,7 +19,7 @@ public function setOverwrite(array $overwrite): void {
 		$this->overWrite = $overwrite;
 	}
 
-	public function getValue(string $app, string $key, ?string $default = null): string {
+	public function getValue($app, $key, $default = null) {
 		if (isset($this->overWrite[$app]) && isset($this->overWrite[$app][$key])) {
 			return $this->overWrite[$app][$key];
 		}