Fix for URL widget uneditable when reverted to null

[SDScandrettKint]

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Description of Change

The issue occurs when this.value is reset to null. When the url and/or url_label are populated, this.value is no longer observable, instead the respective inner properties are the observables. The current subscribe line only updates this.value when it is observable, therefore subscribe back to null for the url and url_label properties doesn't occur.

Issues Solved

Closes #10796

Checklist

• I targeted one of these branches:
  • dev/8.0.x (under development): features, bugfixes not covered below
  • dev/7.6.x (main support): regressions, crashing bugs, security issues, major bugs in new features
  • dev/6.2.x (extended support): major security issues, data loss issues
• I added a changelog in arches/releases
• I submitted a PR to arches-docs (if appropriate)
• Unit tests pass locally with my changes
• I added tests that prove my fix is effective or that my feature works
• My test fails on the target branch

Accessibility Checklist

Developer Guide

Topic	Changed	Retested
Color contrast
Form fields
Headings
Links
Keyboard
Responsive Design
HTML validation
Screen reader

Ticket Background

• Sponsored by: Knowledge Integration
• Found by: @jacobtylerwalls
• Tested by: @SDScandrettKint
• Designed by: @SDScandrettKint

Further comments