build(deps): bump Serilog from 2.8.0 to 2.9.0 (#417)

Bumps [Serilog](https://github.com/serilog/serilog) from 2.8.0 to 2.9.0.
- [Release notes](https://github.com/serilog/serilog/releases)
- [Changelog](https://github.com/serilog/serilog/blob/dev/CHANGES.md)
- [Commits](serilog/serilog@v2.8.0...v2.9.0)

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

src/Splat.Serilog/Splat.Serilog.csproj

@@ -9,7 +9,7 @@
     <PackageId>Splat.Serilog</PackageId>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="Serilog" Version="2.8.0" />
+    <PackageReference Include="Serilog" Version="2.9.0" />
     <PackageReference Include="System.Collections.Immutable" Version="1.6.0" />
   </ItemGroup>
   <ItemGroup>