Set encode false on gulp copy tasks

Gulp v5 streams now default to UTF-8 encoding.
"Most usage of gulp won’t need to change anything, but certain plugins may produce non-UTF-8 output and you’ll need to set `{ encoding: false }` on your gulp streams."

It appears images and fonts (gulpjs/gulp#2790) get affected hence our test was failing https://concourse.notify.tools/builds/114181855#L666d232d:1367

Author: kr8n3r

gulpfile.js

@@ -45,12 +45,12 @@ if (process.env.NOTIFY_ENVIRONMENT == 'development') { // pass through if on dev
 
 const copy = {
   error_pages: () => {
-    return src(paths.src + 'error_pages/**/*')
+    return src(paths.src + 'error_pages/**/*', { encoding: false })
       .pipe(dest(paths.dist + 'error_pages/'))
   },
   govuk_frontend: {
     fonts: () => {
-      return src(paths.govuk_frontend + 'govuk/assets/fonts/**/*')
+      return src(paths.govuk_frontend + 'govuk/assets/fonts/**/*', { encoding: false })
         .pipe(dest(paths.dist + 'fonts/'));
     },
     header_icon_manifest: () => {