Merge branch '5.4' into 6.0

* 5.4:
  Update filesystem.rst

Author: javiereguiluz

components/filesystem.rst

@@ -307,10 +307,16 @@ The ``file.txt`` file contains ``Hello World`` now.
 contents at the end of some file::
 
     $filesystem->appendToFile('logs.txt', 'Email sent to user@example.com');
+    // the third argument tells whether the file should be locked when writing to it
+    $filesystem->appendToFile('logs.txt', 'Email sent to user@example.com', true);
 
 If either the file or its containing directory doesn't exist, this method
 creates them before appending the contents.
 
+.. versionadded:: 5.4
+
+    The third argument of ``appendToFile()`` was introduced in Symfony 5.4.
+
 Error Handling
 --------------