Bump Nerdbank.GitVersioning from 3.4.244 to 3.4.255 in /Rx.NET/Source

Bumps [Nerdbank.GitVersioning](https://github.com/dotnet/Nerdbank.GitVersioning) from 3.4.244 to 3.4.255.
- [Release notes](https://github.com/dotnet/Nerdbank.GitVersioning/releases)
- [Commits](https://github.com/dotnet/Nerdbank.GitVersioning/commits)

---
updated-dependencies:
- dependency-name: Nerdbank.GitVersioning
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

Rx.NET/Source/Directory.build.props

@@ -28,7 +28,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All"/>
-    <PackageReference Include="Nerdbank.GitVersioning" Version="3.4.244" PrivateAssets="all" />
+    <PackageReference Include="Nerdbank.GitVersioning" Version="3.4.255" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(IsTestProject)' == 'true'">