### 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)

ERR_FAIL_COND_MSG(!tiles.has(p_atlas_coords), vformat("TileSetAtlasSource has no tile at %s.", Vector2i(p_atlas_coords)));
	tiles[p_atlas_coords].animation_mode = p_mode;
	emit_signal(SNAME("changed"));
}
TileSetAtlasSource::TileAnimationMode TileSetAtlasSource::get_tile_animation_mode(const Vector2i p_atlas_coords) const {
	ERR_FAIL_COND_V_MSG(!tiles.has(p_atlas_coords), TILE_ANIMATION_MODE_DEFAULT, vformat("TileSetAtlasSource has no tile at %s.", Vector2i(p_atlas_coords)));
	return tiles[p_atlas_coords].animation_mode;
}
void TileSetAtlasSource::set_tile_animation_frames_count(const Vector2i p_atlas_coords, int p_frames_count) {
	ERR_FAIL_COND_MSG(!tiles.has(p_atlas_coords), vformat("TileSetAtlasSource has no tile at %s.", Vector2i(p_atlas_coords)));
	ERR_FAIL_COND(p_frames_count < 1);
	int old_size = tiles[p_atlas_coords].animation_frames_durations.size();
	if (p_frames_count == old_size) {
		return;
	}
	TileAlternativesData &tad = tiles[p_atlas_coords];
	bool room_for_tile = has_room_for_tile(p_atlas_coords, tad.size_in_atlas, tad.animation_columns, tad.animation_separation, p_frames_count, p_atlas_coords);
	ERR_FAIL_COND_MSG(!room_for_tile, "Cannot set animation columns count, tiles are already present in the space the tile would cover.");
	_clear_coords_mapping_cache(p_atlas_coords);
	tiles[p_atlas_coords].animation_frames_durations.resize(p_frames_count);
	for (int i = old_size; i < p_frames_count; i++) {
		tiles[p_atlas_coords].animation_frames_durations[i] = 1.0;
	}
	_create_coords_mapping_cache(p_atlas_coords);
	_queue_update_padded_texture();
	notify_property_list_changed();
	emit_signal(SNAME("changed"));
}
int TileSetAtlasSource::get_tile_animation_frames_count(const Vector2i p_atlas_coords) const {