Only scan src in client directory for Tailwind to prevent unnecessary…

… rebuilds

https://tailwindcss.com/docs/content-configuration#styles-rebuild-in-an-infinite-loop

This speeds up the FE production build from 60s to ~21s on my machine, and also speeds up hot rebuilds to just ~3s

tailwind.config.js

@@ -8,7 +8,12 @@ module.exports = {
   content: [
     './wagtail/**/*.{py,html,ts,tsx}',
     './wagtail/**/static_src/**/*.js',
-    './client/**/*.{js,ts,tsx,mdx}',
+    // Make sure NOT to include the `client/scss` directory,
+    // even if we don't specify `*.scss` files here.
+    // The directory would still be scanned for files, which would cause
+    // the styles to rebuild in a loop.
+    // https://tailwindcss.com/docs/content-configuration#styles-rebuild-in-an-infinite-loop
+    './client/src/**/*.{js,ts,tsx,mdx}',
     './docs/**/*.{md,rst}',
   ],
   corePlugins: {