Doc: Fix typo in File documentation

Fixes #19383.

doc/classes/File.xml

@@ -9,13 +9,13 @@
 		[codeblock]
 		func save(content):
 		    var file = File.new()
-		    file.open("user://save_game.dat", file.WRITE)
+		    file.open("user://save_game.dat", File.WRITE)
 		    file.store_string(content)
 		    file.close()
 
 		func load():
 		    var file = File.new()
-		    file.open("user://save_game.dat", file.READ)
+		    file.open("user://save_game.dat", File.READ)
 		    var content = file.get_as_text()
 		    file.close()
 		    return content