Fix widget.disabled handling of value change of equal truthiness

[tshirtman]

Comparing for equality is too strict, when what we want is to know if
thue value is Truthy or Falsy, this mismatch in condition created cases
where a widget was set to disabled, but wasn't, as well as widgets
staying disabled, when they should have been enabled again.

Maintainer merge checklist

• Title is descriptive/clear for inclusion in release notes.
• Applied a Component: xxx label.
• Applied the api-deprecation or api-break label.
• Applied the release-highlight label to be highlighted in release notes.
• Added to the milestone version it was merged into.
• Unittests are included in PR.
• Properly documented, including versionadded, versionchanged as needed.