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

@@ -50,7 +50,7 @@ const copy = {
   },
   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/'));
     },
   }
@@ -161,7 +161,7 @@ const images = () => {
   return src([
       paths.src + 'images/**/*',
       paths.govuk_frontend + 'govuk/assets/images/**/*'
-    ])
+    ],{ encoding: false })
     .pipe(dest(paths.dist + 'images/'))
 };