Fix variable name for referenced variable.

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>

psalm.xml

@@ -49,8 +49,8 @@
 		</UndefinedFunction>
 		<UndefinedGlobalVariable>
 			<errorLevel type="suppress">
-				<referencedVariable name="l" />
-				<referencedVariable name="_" />
+				<referencedVariable name="$l"/>
+				<referencedVariable name="$_"/>
 				<!-- false positive: https://github.com/nextcloud/server/blob/cb057829f72c70e819f456edfadbb29d72dba832/lib/private/Console/Application.php#L92 -->
 				<file name="apps/*/appinfo/register_command.php" />
 				<file name="core/register_command.php" />