Bump System.Threading.Tasks.Dataflow from 7.0.0 to 8.0.0 (#1292)

Bumps [System.Threading.Tasks.Dataflow](https://github.com/dotnet/runtime) from 7.0.0 to 8.0.0.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v7.0.0...v8.0.0)

---
updated-dependencies:
- dependency-name: System.Threading.Tasks.Dataflow
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Directory.Packages.props

@@ -38,7 +38,7 @@
     <PackageVersion Include="System.Drawing.Common" Version="8.0.0" />
     <PackageVersion Include="System.Memory" Version="4.5.5" />
     <PackageVersion Include="System.Runtime.CompilerServices.Unsafe" Version="6.0.0" />
-    <PackageVersion Include="System.Threading.Tasks.Dataflow" Version="7.0.0" />
+    <PackageVersion Include="System.Threading.Tasks.Dataflow" Version="8.0.0" />
     <PackageVersion Include="System.Threading.Tasks.Extensions" Version="4.5.4" />
     <PackageVersion Include="System.ValueTuple" Version="4.5.0" />
     <PackageVersion Include="xunit.abstractions" Version="2.0.3" />