Memory leak in MahApps.Templates.ValidationError

[lipchev]

Describe the bug

There is a minor memory leak with the default validation error template (MahApps.Templates.ValidationError): the binding mode on this line should be OneTime, as the underlying object (System.Windows.Controls.ValidationError) does not implement INotifyPropertyChanged

Steps to reproduce

Make the red validation popup appear by hovering over a control with a validation error.

Actual behavior

Observed the WPF binding leak is detected by the memory profiler

Environment

MahApps.Metro version: v2.0.0
Windows build number: Win10 1909 [Version 10.0.18363.836]
Visual Studio: 2019 16.6.0
Target Framework: .Net Core 3.1 (v4.5.2, v4.7.2)

Screenshots

[punker76]

@lipchev Thx for reporting this! If you want to fix this, then create a PR. I'll appreciate it! 👍