Mastodon nginx: simplify some regexes

installation/mastodon.conf

@@ -91,7 +91,7 @@ server {
   # Mastodon public files.
   # https://github.com/mastodon/mastodon/tree/main/public
   # Take only what we need for Soapbox.
-  location ~ ^/(assets|favicon.ico|browserconfig.xml|embed.js|android-chrome-192x192.png|apple-touch-icon.png|avatars/original/missing.png|headers/original/missing.png) {
+  location ~ ^/(assets|favicon.(ico|png)|browserconfig.xml|embed.js|android-chrome-192x192.png|apple-touch-icon.png|(avatars|headers)/original/missing.png) {
     root /home/mastodon/live/public;
     add_header Cache-Control "public, max-age=31536000, immutable";
     add_header Strict-Transport-Security "max-age=31536000" always;