Bump DiffPlex from 1.4.4 to 1.5.0 in /Rx.NET/Source

Bumps [DiffPlex](https://github.com/mmanela/diffplex) from 1.4.4 to 1.5.0.
- [Release notes](https://github.com/mmanela/diffplex/releases)
- [Commits](https://github.com/mmanela/diffplex/commits)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Rx.NET/Source/tests/Tests.System.Reactive.ApiApprovals/Tests.System.Reactive.ApiApprovals.csproj

@@ -32,7 +32,7 @@
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.1" />
     <PackageReference Include="ApprovalTests" Version="4.4.0" />
-    <PackageReference Include="DiffPlex" Version="1.4.4" />
+    <PackageReference Include="DiffPlex" Version="1.5.0" />
     <PackageReference Include="PublicApiGenerator" Version="9.3.0" />
   </ItemGroup>