build(deps): bump ReactiveUI.Binding to 8.8.0

[glennawatson]

Summary

ReactiveUI now builds against ReactiveUI.Binding 8.8.0.

• BindingVersion in Directory.Packages.props is now 8.8.0.
• Generated view bindings onto a control the view holds in a field, such as a control named in XAML, follow the view's current view model. A view can bind before it has one.
• A float bound to text through the runtime converter formats with the invariant culture, as a generated binding does.

Why

ReactiveUI.Avalonia and ReactiveUI.Uno move to ReactiveUI.Binding 8.8.0, which fixes generated bindings on Uno controls and on field controls. ReactiveUI references the same version so the platform packages do not pull it onto one it was never built against.

Breaking changes

None in ReactiveUI. ReactiveUI.Binding 8.8.0 formats a float with no conversion hint in the invariant culture, so an app in a culture with a decimal comma sees 7.25 where it saw 7,25.

How this was verified

Built the whole solution and ran the test projects CI runs on Linux. The Windows-only test projects run in CI.

Notes for the reviewer

A version bump only.

Checklist

• I have read the Contribute guide
• The PR title follows Conventional Commits
• Tests cover this change, or the summary says why they do not
• New or changed public API has XML documentation

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.69%. Comparing base (0b69014) to head (a2ea52e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4530   +/-   ##
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  Coverage   93.69%   93.69%           
=======================================
  Files         175      175           
  Lines        6231     6231           
  Branches      743      743           
=======================================
  Hits         5838     5838           
  Misses        392      392           
  Partials        1        1           

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