### 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)

if (physics_layers[i].collision_mask == 1) {
			property_info.usage ^= PROPERTY_USAGE_STORAGE;
		}
		p_list->push_back(property_info);
		
		property_info = PropertyInfo(Variant::OBJECT, vformat("physics_layer_%d/physics_material", i), PROPERTY_HINT_RESOURCE_TYPE, "PhysicsMaterial");
		if (!physics_layers[i].physics_material.is_valid()) {
			property_info.usage ^= PROPERTY_USAGE_STORAGE;
		}
		p_list->push_back(property_info);
	}
	
	p_list->push_back(PropertyInfo(Variant::NIL, GNAME("Terrains", ""), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_GROUP));
	for (int terrain_set_index = 0; terrain_set_index < terrain_sets.size(); terrain_set_index++) {
		p_list->push_back(PropertyInfo(Variant::INT, vformat("terrain_set_%d/mode", terrain_set_index), PROPERTY_HINT_ENUM, "Match Corners and Sides,Match Corners,Match Sides"));
		p_list->push_back(PropertyInfo(Variant::NIL, vformat("terrain_set_%d/terrains", terrain_set_index), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_EDITOR | PROPERTY_USAGE_ARRAY, vformat("terrain_set_%d/terrain_", terrain_set_index)));
		for (int terrain_index = 0; terrain_index < terrain_sets[terrain_set_index].terrains.size(); terrain_index++) {
			p_list->push_back(PropertyInfo(Variant::STRING, vformat("terrain_set_%d/terrain_%d/name", terrain_set_index, terrain_index)));
			p_list->push_back(PropertyInfo(Variant::COLOR, vformat("terrain_set_%d/terrain_%d/color", terrain_set_index, terrain_index)));
		}
	}
	
	p_list->push_back(PropertyInfo(Variant::NIL, GNAME("Navigation", ""), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_GROUP));
	for (int i = 0; i < navigation_layers.size(); i++) {
		p_list->push_back(PropertyInfo(Variant::INT, vformat("navigation_layer_%d/layers", i), PROPERTY_HINT_LAYERS_2D_NAVIGATION));
	}
	
	String argt = "Any";
	for (int i = 1; i < Variant::VARIANT_MAX; i++) {
		argt += "," + Variant::get_type_name(Variant::Type(i));