### 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)

property_info = PropertyInfo(Variant::BOOL, vformat("physics_layer_%d/polygon_%d/%s", i, j, PNAME("one_way")));
				if (physics[i].polygons[j].one_way == false) {
					property_info.usage ^= PROPERTY_USAGE_STORAGE;
				}
				p_list->push_back(property_info);
				
				property_info = PropertyInfo(Variant::FLOAT, vformat("physics_layer_%d/polygon_%d/%s", i, j, PNAME("one_way_margin")));
				if (physics[i].polygons[j].one_way_margin == 1.0) {
					property_info.usage ^= PROPERTY_USAGE_STORAGE;
				}
				p_list->push_back(property_info);
			}
		}
		
		if (terrain_set >= 0) {
			p_list->push_back(PropertyInfo(Variant::NIL, GNAME("Terrains", ""), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_GROUP));
			for (int i = 0; i < TileSet::CELL_NEIGHBOR_MAX; i++) {
				TileSet::CellNeighbor bit = TileSet::CellNeighbor(i);
				if (is_valid_terrain_peering_bit(bit)) {
					property_info = PropertyInfo(Variant::INT, vformat("%s/%s", PNAME("terrains_peering_bit"), TileSet::CELL_NEIGHBOR_ENUM_TO_TEXT[i]));
					if (get_terrain_peering_bit(bit) == -1) {
						property_info.usage ^= PROPERTY_USAGE_STORAGE;
					}
					p_list->push_back(property_info);
				}
			}
		}
		
		p_list->push_back(PropertyInfo(Variant::NIL, GNAME("Navigation", ""), PROPERTY_HINT_NONE, "", PROPERTY_USAGE_GROUP));
		for (int i = 0; i < navigation.size(); i++) {