Bump gulp-sass

Intended to deal with this security vulnerability:

https://github.blog/2021-09-08-github-security-update-vulnerabilities-tar-npmcli-arborist/

Bumping gulp-sass to version 5 removes its
dependency on the tar package mentioned in that
article.

Version 5 requires you to specify a compiler
directly in the gulpfile so that code is changed
in line with this guidance:

https://github.com/dlmanning/gulp-sass/tree/master#migrating-to-version-5

Note: node-sass is now deprecated so this also
changes the sass compiler gulp-sass uses to
dart-sass (aka 'sass'), the compiler now
recommended by the Sass project:

https://sass-lang.com/dart-sass

This also bumps gulp and all its plugin modules to
their latest versions, for parity.

gulpfile.js

@@ -20,7 +20,7 @@ plugins.cssUrlAdjuster = require('gulp-css-url-adjuster');
 plugins.jshint = require('gulp-jshint');
 plugins.prettyerror = require('gulp-prettyerror');
 plugins.rollup = require('gulp-better-rollup')
-plugins.sass = require('gulp-sass');
+plugins.sass = require('gulp-sass')(require('sass'));
 plugins.sassLint = require('gulp-sass-lint');
 plugins.uglify = require('gulp-uglify');
 
@@ -207,8 +207,7 @@ const sass = () => {
       paths.src + '/stylesheets/print.scss'
     ])
     .pipe(plugins.prettyerror())
-    .pipe(plugins.sass({
-      outputStyle: 'nested',
+    .pipe(plugins.sass.sync({
       includePaths: [
         paths.npm + 'govuk-elements-sass/public/sass/',
         paths.toolkit + 'stylesheets/',

package.json

@@ -27,20 +27,21 @@
     "govuk_frontend_toolkit": "8.1.0",
     "govuk-elements-sass": "3.1.2",
     "govuk-frontend": "2.13.0",
-    "gulp": "4.0.0",
+    "gulp": "4.0.2",
     "gulp-add-src": "1.0.0",
     "gulp-babel": "8.0.0",
     "gulp-better-rollup": "4.0.1",
-    "gulp-clean-css": "4.2.0",
+    "gulp-clean-css": "4.3.0",
     "gulp-concat": "2.6.1",
-    "gulp-include": "2.3.1",
-    "gulp-sass": "4.0.2",
+    "gulp-include": "2.4.1",
+    "gulp-sass": "5.0.0",
     "gulp-uglify": "3.0.2",
     "hogan": "1.0.2",
     "jquery": "3.5.0",
     "leaflet": "1.6.0",
     "query-command-supported": "1.0.0",
     "rollup": "1.23.1",
+    "sass": "1.32.7",
     "streamqueue": "1.1.2",
     "textarea-caret": "3.1.0",
     "timeago": "1.6.5"
@@ -48,7 +49,7 @@
   "devDependencies": {
     "gulp-css-url-adjuster": "0.2.3",
     "gulp-jshint": "2.1.0",
-    "gulp-prettyerror": "1.2.1",
+    "gulp-prettyerror": "2.0.0",
     "gulp-sass-lint": "1.4.0",
     "jest": "24.7.1",
     "jest-date-mock": "^1.0.8",