chore(deps): update dependency testableio.system.io.abstractions.testinghelpers to v19.2.64

This PR contains the following updates:

Package	Type	Update	Change
TestableIO.System.IO.Abstractions.TestingHelpers	nuget	patch	`19.2.61` -> `19.2.64`

Release Notes

TestableIO/System.IO.Abstractions (TestableIO.System.IO.Abstractions.TestingHelpers)

### [`v19.2.64`](https://togithub.com/TestableIO/System.IO.Abstractions/releases/tag/v19.2.64) #### What's Changed - feat: add `Null` to MockFileStream to shadow the static `Stream.Null` field by [@vbreuss](https://togithub.com/vbreuss) in [https://github.com/TestableIO/System.IO.Abstractions/pull/1025](https://togithub.com/TestableIO/System.IO.Abstractions/pull/1025) **Full Changelog**: https://github.com/TestableIO/System.IO.Abstractions/compare/v19.2.63...v19.2.64 ### [`v19.2.63`](https://togithub.com/TestableIO/System.IO.Abstractions/releases/tag/v19.2.63) #### What's Changed - refactor: use `CommonExceptions` to create exceptions by [@vbreuss](https://togithub.com/vbreuss) in [https://github.com/TestableIO/System.IO.Abstractions/pull/1027](https://togithub.com/TestableIO/System.IO.Abstractions/pull/1027) - fix: use full path in `Directory.SetCurrentDirectory` by [@vbreuss](https://togithub.com/vbreuss) in [https://github.com/TestableIO/System.IO.Abstractions/pull/1028](https://togithub.com/TestableIO/System.IO.Abstractions/pull/1028) **Full Changelog**: https://github.com/TestableIO/System.IO.Abstractions/compare/v19.2.61...v19.2.63