### Godot version

5ee983188de97ae027f9b9c1443438063f708a7e

### System information

Windows 11

### Issue description

Godot editor will throw an error and fail to generate preview icons for terrain tiles which use a base image which is not RGBA8 format.
`core\io\image.cpp:2788 - Condition "format != p_src->format" is true.`

### Steps to reproduce

- Import a non-RGBA8 image into Godot.
- Create a TileMap
- Create an associated TileSet
- Create a terrain for this tileset
- Add the image as an atlas
- Go to the paint tab
- Paint the terrain on the TileSet
- An error will occur any time terrains are edited in the TileSet editor or selected in the TileMap editor terrain tab.

### Minimal reproduction project

[tileset_terrain_bug.zip](https://github.com/godotengine/godot/files/13264213/tileset_terrain_bug.zip)

PropertyInfo property_info;
	
	if (tile_set) {
		
		p_list->push_back(PropertyInfo(Variant::NIL, GNAME("Rendering", ""), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_GROUP));
		for (int i = 0; i < occluders.size(); i++) {
			
			property_info = PropertyInfo(Variant::OBJECT, vformat("occlusion_layer_%d/%s", i, PNAME("polygon")), PROPERTY_HINT_RESOURCE_TYPE, "OccluderPolygon2D", PROPERTY_USAGE_DEFAULT);
			if (!occluders[i].is_valid()) {
				property_info.usage ^= PROPERTY_USAGE_STORAGE;
			}
			p_list->push_back(property_info);
		}
		
		p_list->push_back(PropertyInfo(Variant::NIL, GNAME("Physics", ""), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_GROUP));
		for (int i = 0; i < physics.size(); i++) {
			p_list->push_back(PropertyInfo(Variant::VECTOR2, vformat("physics_layer_%d/%s", i, PNAME("linear_velocity")), PROPERTY_HINT_NONE));
			p_list->push_back(PropertyInfo(Variant::FLOAT, vformat("physics_layer_%d/%s", i, PNAME("angular_velocity")), PROPERTY_HINT_NONE));
			p_list->push_back(PropertyInfo(Variant::INT, vformat("physics_layer_%d/%s", i, PNAME("polygons_count")), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_EDITOR));
			for (int j = 0; j < physics[i].polygons.size(); j++) {
				
				property_info = PropertyInfo(Variant::ARRAY, vformat("physics_layer_%d/polygon_%d/%s", i, j, PNAME("points")), PROPERTY_HINT_ARRAY_TYPE, "Vector2", PROPERTY_USAGE_DEFAULT);
				if (physics[i].polygons[j].polygon.is_empty()) {
					property_info.usage ^= PROPERTY_USAGE_STORAGE;
				}
				p_list->push_back(property_info);