### 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)

Size2 size = get_tile_texture_region(p_atlas_coords).size;
	Rect2 rect = Rect2(-size / 2 - get_tile_data(p_atlas_coords, p_alternative_tile)->get_texture_origin(), size);
	return rect.has_point(p_position);
}
int TileSetAtlasSource::alternative_no_transform(int p_alternative_id) {
	return p_alternative_id & ~(TRANSFORM_FLIP_H | TRANSFORM_FLIP_V | TRANSFORM_TRANSPOSE);
}
Ref<Texture2D> TileSetAtlasSource::get_runtime_texture() const {
	if (use_texture_padding) {
		return padded_texture;
	} else {
		return texture;
	}
}
Rect2i TileSetAtlasSource::get_runtime_tile_texture_region(Vector2i p_atlas_coords, int p_frame) const {
	ERR_FAIL_COND_V_MSG(!tiles.has(p_atlas_coords), Rect2i(), vformat("TileSetAtlasSource has no tile at %s.", String(p_atlas_coords)));
	ERR_FAIL_INDEX_V(p_frame, (int)tiles[p_atlas_coords].animation_frames_durations.size(), Rect2i());
	Rect2i src_rect = get_tile_texture_region(p_atlas_coords, p_frame);
	if (use_texture_padding) {
		const TileAlternativesData &tad = tiles[p_atlas_coords];
		Vector2i frame_coords = p_atlas_coords + (tad.size_in_atlas + tad.animation_separation) * ((tad.animation_columns > 0) ? Vector2i(p_frame % tad.animation_columns, p_frame / tad.animation_columns) : Vector2i(p_frame, 0));
		Vector2i base_pos = frame_coords * (texture_region_size + Vector2i(2, 2)) + Vector2i(1, 1);
		return Rect2i(base_pos, src_rect.size);
	} else {
		return src_rect;
	}
}
void TileSetAtlasSource::move_tile_in_atlas(Vector2i p_atlas_coords, Vector2i p_new_atlas_coords, Vector2i p_new_size) {