Fix compression-webpack-plugin configuration (#16356)
Fix compression-webpack-plugin configuration (#16356)

compression-webpack-plugin 6.0.0 has changed how filenames were generated,
so from #14892 onward (Mastodon v3.3.0 and later), compressed files were
output to a file named `.gz` instead of the correct filenames.
gol-cha/mastodon,gol-cha/mastodon,gol-cha/mastodon,gol-cha/mastodon