Fix HTML escaping for partner email sharing

[aduth]

🛠 Summary of changes

Fixes an issue where partner email selection text was showing as escaped HTML.

The content was recently updated in #11468 to add HTML, and while the string key is correctly suffixed with _html, one of two views uses I18n.t instead of t, which does not perform automatic unescaping (docs).

📜 Testing Plan

Verify the text does not show escaped HTML:

1. Run sample application in parallel to IdP
2. Prerequisite: If you've already consented with partner application, sign in and revoke consent from "Connected Accounts" account page
3. Go to http://localhost:9292
4. Click "Sign in"
5. Complete sign-in up to consent screen
6. Click "Change" if you see it. Otherwise, click "Add new email" and complete this flow
7. Observe introduction paragraph of email selection screen does not include escaped HTML

👀 Screenshots

Before	After

[aduth]

I added a custom Rubocop linter in 563fa02, since it seems easy enough to flag calls to I18n.t with a string key ending with _html.

I had to limit this to apply only to views for now, since there's a lot of false positives in the backend Ruby code, particularly for error messages that are created with I18n.t and marked as safe after-the-fact.