Fix FXIOS-10626 - Use separate string for sites without a domain in calendar alert

[issammani]

:scroll: Tickets

Jira ticket Github issue

:bulb: Description

This PR:

• Add seperate BodyDefault string instead of using a default domain and concatenating.

For context see: https://github.com/mozilla-mobile/firefox-ios/pull/23232#issuecomment-2488960898

:pencil: Checklist

You have to check all boxes before merging

• [x] Filled in the above information (tickets numbers and description of your work)
• [x] Updated the PR name to follow our PR naming guidelines
• [ ] Wrote unit tests and/or ensured the tests suite is passing
• [ ] When working on UI, I checked and implemented accessibility (minimum Dynamic Text and VoiceOver)
• [ ] If needed, I updated documentation / comments for complex code and public methods
• [ ] If needed, added a backport comment (example @Mergifyio backport release/v120)

[mobiletest-ci-bot]

	Messages
:book:	Project coverage: 33.04%
:book:	Edited 2 files
:book:	Created 0 files

Client.app: Coverage: 31.13

File	Coverage
BrowserViewController+WebViewDelegates.swift	4.44%	⚠️

Generated by :no_entry_sign: Danger Swift against cd598ad43a62d2ae7beea88cc77fc80203cf9d66

[issammani]

Merging since generic BR is green and the only failing tests are testUpdateAllAddressFields() and testAddNewAddressAllFieldsFilled() which are also failing on main.