Bump gulp-sass from 5.1.0 to 6.0.0

Bumps [gulp-sass](https://github.com/dlmanning/gulp-sass) from 5.1.0 to 6.0.0.
- [Release notes](https://github.com/dlmanning/gulp-sass/releases)
- [Changelog](https://github.com/dlmanning/gulp-sass/blob/master/CHANGELOG.md)
- [Commits](dlmanning/gulp-sass@v5.1.0...v6.0.0)

---
updated-dependencies:
- dependency-name: gulp-sass
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -33,7 +33,7 @@
     "gulp-clean-css": "^4.3.0",
     "gulp-nodemon": "^2.5.0",
     "gulp-rename": "^2.0.0",
-    "gulp-sass": "^5.1.0",
+    "gulp-sass": "^6.0.0",
     "lodash": "^4.17.21",
     "nhsuk-frontend": "^9.1.0",
     "nunjucks": "^3.2.4",