Fix deprecation warnings on white_list_sanitizer

[mpw5]

What

The recent update to v1.1.0 of rails_html_sanitizer means that rspec is raising lots of unnecessary deprecation warnings. This is a bug in that version and and is resolved by updating to v1.2.0.

See issue and suggested fix here: rails/rails#36858

Checklist

Before you ask people to review this PR:

• Tests and rubocop should be passing: bundle exec rake
• Github should not be reporting conflicts; you should have recently run git rebase master.
• There should be no unnecessary whitespace changes. These make diffs harder to read and conflicts more likely.
• The PR description should say what you changed and why, with a link to the JIRA story.
• You should have looked at the diff against master and ensured that nothing unexpected is included in your changes.
• You should have checked that the commit messages say why the change was made.