build(deps): bump Mindscape.Raygun4Net from 5.13.0 to 6.0.3 in /src

Bumps [Mindscape.Raygun4Net](https://github.com/MindscapeHQ/raygun4net) from 5.13.0 to 6.0.3.
- [Release notes](https://github.com/MindscapeHQ/raygun4net/releases)
- [Commits](https://github.com/MindscapeHQ/raygun4net/commits)

---
updated-dependencies:
- dependency-name: Mindscape.Raygun4Net
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

src/Splat.Raygun/Splat.Raygun.csproj

@@ -30,7 +30,7 @@
     </When>
     <When Condition=" $(TargetFramework.StartsWith('net4')) ">
       <ItemGroup>
-        <PackageReference Include="Mindscape.Raygun4Net" Version="5.13.0" />
+        <PackageReference Include="Mindscape.Raygun4Net" Version="6.0.3" />
       </ItemGroup>
     </When>
   </Choose>