Bump rubocop from 1.35.1 to 1.56.2

Among many things, this version includes updates in the
`Layout/ExtraSpacing`, `Layout/SpaceAroundOperators` and
`Style/RedundantReturn` rules, which means we need to update the code in
some places in order to follow these rules.

Bumps [rubocop](https://github.com/rubocop/rubocop) from 1.35.1 to 1.56.2.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop/rubocop/compare/v1.35.1...v1.56.2)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

spec/models/setting_spec.rb

@@ -171,7 +171,7 @@ describe Setting do
 
   describe ".accepted_content_types_for" do
     it "returns the formats accepted according to the setting value" do
-      Setting["uploads.images.content_types"] =    "image/jpeg image/gif"
+      Setting["uploads.images.content_types"] = "image/jpeg image/gif"
       Setting["uploads.documents.content_types"] = "application/pdf application/msword"
 
       expect(Setting.accepted_content_types_for("images")).to    eq ["jpg", "gif"]