Bump System.IO.Abstractions.TestingHelpers from 19.2.51 to 20.0.4

Bumps [System.IO.Abstractions.TestingHelpers](https://github.com/TestableIO/System.IO.Abstractions) from 19.2.51 to 20.0.4.
- [Release notes](https://github.com/TestableIO/System.IO.Abstractions/releases)
- [Commits](TestableIO/System.IO.Abstractions@v19.2.51...v20.0.4)

---
updated-dependencies:
- dependency-name: System.IO.Abstractions.TestingHelpers
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Directory.Packages.props

@@ -16,6 +16,6 @@
     <PackageVersion Include="coverlet.collector" Version="6.0.0" />
     <PackageVersion Include="System.CommandLine" Version="2.0.0-beta4.22272.1" />
     <PackageVersion Include="System.IO.Abstractions" Version="20.0.4" />
-    <PackageVersion Include="System.IO.Abstractions.TestingHelpers" Version="19.2.51" />
+    <PackageVersion Include="System.IO.Abstractions.TestingHelpers" Version="20.0.4" />
   </ItemGroup>
 </Project>