Bump Serilog from 2.12.0 to 3.1.1

Bumps [Serilog](https://github.com/serilog/serilog) from 2.12.0 to 3.1.1.
- [Release notes](https://github.com/serilog/serilog/releases)
- [Commits](serilog/serilog@v2.12.0...v3.1.1)

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

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

source/Serilog.Sink.AppCenter.Tests/Serilog.Sink.AppCenter.Tests.csproj

@@ -18,7 +18,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="Serilog" Version="2.12.0" />
+    <PackageReference Include="Serilog" Version="3.1.1" />
   </ItemGroup>
 
   <ItemGroup>

source/Serilog.Sink.AppCenter/Serilog.Sink.AppCenter.csproj

@@ -18,7 +18,7 @@
 	</PropertyGroup>
 
 	<ItemGroup>
-		<PackageReference Include="Serilog" Version="2.12.0"/>
+		<PackageReference Include="Serilog" Version="3.1.1"/>
 		<PackageReference Include="Microsoft.AppCenter.Analytics" Version="5.0.3"/>
 		<PackageReference Include="Microsoft.AppCenter.Crashes" Version="5.0.2"/>
 	</ItemGroup>