### 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)

ClassDB::bind_method(D_METHOD("set_tile_animation_speed", "atlas_coords", "speed"), &TileSetAtlasSource::set_tile_animation_speed);
	ClassDB::bind_method(D_METHOD("get_tile_animation_speed", "atlas_coords"), &TileSetAtlasSource::get_tile_animation_speed);
	ClassDB::bind_method(D_METHOD("set_tile_animation_mode", "atlas_coords", "mode"), &TileSetAtlasSource::set_tile_animation_mode);
	ClassDB::bind_method(D_METHOD("get_tile_animation_mode", "atlas_coords"), &TileSetAtlasSource::get_tile_animation_mode);
	ClassDB::bind_method(D_METHOD("set_tile_animation_frames_count", "atlas_coords", "frames_count"), &TileSetAtlasSource::set_tile_animation_frames_count);
	ClassDB::bind_method(D_METHOD("get_tile_animation_frames_count", "atlas_coords"), &TileSetAtlasSource::get_tile_animation_frames_count);
	ClassDB::bind_method(D_METHOD("set_tile_animation_frame_duration", "atlas_coords", "frame_index", "duration"), &TileSetAtlasSource::set_tile_animation_frame_duration);
	ClassDB::bind_method(D_METHOD("get_tile_animation_frame_duration", "atlas_coords", "frame_index"), &TileSetAtlasSource::get_tile_animation_frame_duration);
	ClassDB::bind_method(D_METHOD("get_tile_animation_total_duration", "atlas_coords"), &TileSetAtlasSource::get_tile_animation_total_duration);
	
	ClassDB::bind_method(D_METHOD("create_alternative_tile", "atlas_coords", "alternative_id_override"), &TileSetAtlasSource::create_alternative_tile, DEFVAL(INVALID_TILE_ALTERNATIVE));
	ClassDB::bind_method(D_METHOD("remove_alternative_tile", "atlas_coords", "alternative_tile"), &TileSetAtlasSource::remove_alternative_tile);
	ClassDB::bind_method(D_METHOD("set_alternative_tile_id", "atlas_coords", "alternative_tile", "new_id"), &TileSetAtlasSource::set_alternative_tile_id);
	ClassDB::bind_method(D_METHOD("get_next_alternative_tile_id", "atlas_coords"), &TileSetAtlasSource::get_next_alternative_tile_id);
	ClassDB::bind_method(D_METHOD("get_tile_data", "atlas_coords", "alternative_tile"), &TileSetAtlasSource::get_tile_data);
	
	ClassDB::bind_method(D_METHOD("get_atlas_grid_size"), &TileSetAtlasSource::get_atlas_grid_size);
	ClassDB::bind_method(D_METHOD("get_tile_texture_region", "atlas_coords", "frame"), &TileSetAtlasSource::get_tile_texture_region, DEFVAL(0));
	
	ClassDB::bind_method(D_METHOD("_update_padded_texture"), &TileSetAtlasSource::_update_padded_texture);
	ClassDB::bind_method(D_METHOD("get_runtime_texture"), &TileSetAtlasSource::get_runtime_texture);
	ClassDB::bind_method(D_METHOD("get_runtime_tile_texture_region", "atlas_coords", "frame"), &TileSetAtlasSource::get_runtime_tile_texture_region);
	BIND_ENUM_CONSTANT(TILE_ANIMATION_MODE_DEFAULT)
	BIND_ENUM_CONSTANT(TILE_ANIMATION_MODE_RANDOM_START_TIMES)
	BIND_ENUM_CONSTANT(TILE_ANIMATION_MODE_MAX)
	BIND_CONSTANT(TRANSFORM_FLIP_H)
	BIND_CONSTANT(TRANSFORM_FLIP_V)
	BIND_CONSTANT(TRANSFORM_TRANSPOSE)
}
TileSetAtlasSource::~TileSetAtlasSource() {