Fix feature tag casing in the Windows pen tablet project setting name

Feature tags are case-sensitive.

doc/classes/ProjectSettings.xml

@@ -734,7 +734,7 @@
 		<member name="input_devices/pen_tablet/driver" type="String" setter="" getter="">
 			Specifies the tablet driver to use. If left empty, the default driver will be used.
 		</member>
-		<member name="input_devices/pen_tablet/driver.windows" type="String" setter="" getter="">
+		<member name="input_devices/pen_tablet/driver.Windows" type="String" setter="" getter="">
 			Override for [member input_devices/pen_tablet/driver] on Windows.
 		</member>
 		<member name="input_devices/pointing/emulate_mouse_from_touch" type="bool" setter="" getter="" default="true">

main/main.cpp

@@ -1551,8 +1551,8 @@ Error Main::setup2(Thread::ID p_main_tid_override) {
 
 	{
 		GLOBAL_DEF_RST_NOVAL("input_devices/pen_tablet/driver", "");
-		GLOBAL_DEF_RST_NOVAL("input_devices/pen_tablet/driver.windows", "");
-		ProjectSettings::get_singleton()->set_custom_property_info("input_devices/pen_tablet/driver.windows", PropertyInfo(Variant::STRING, "input_devices/pen_tablet/driver.windows", PROPERTY_HINT_ENUM, "wintab,winink"));
+		GLOBAL_DEF_RST_NOVAL("input_devices/pen_tablet/driver.Windows", "");
+		ProjectSettings::get_singleton()->set_custom_property_info("input_devices/pen_tablet/driver.Windows", PropertyInfo(Variant::STRING, "input_devices/pen_tablet/driver.Windows", PROPERTY_HINT_ENUM, "wintab,winink"));
 	}
 
 	if (tablet_driver == "") { // specified in project.godot