Add dummy generic type so optimizer works with parcel v2.8.0+

Parcel v2.8.0 adds a BundleConfigType generic type to Optimizer
(parcel-bundler/parcel#8370) as part of
their `loadBundleConfig` method. We use a dummy type because we
don't need this functionality currently.

packages/parcel-optimizer/src/index.ts

@@ -16,7 +16,7 @@ const configFiles = [
   'compiledcss.config.js',
 ];
 
-export default new Optimizer<ParcelOptimizerOpts>({
+export default new Optimizer<ParcelOptimizerOpts, unknown>({
   async loadConfig({ config, options }) {
     const conf = await config.getConfigFrom(join(options.projectRoot, 'index'), configFiles, {
       packageKey: '@compiled/parcel-optimizer',