Bump coverlet.msbuild from 2.3.1 to 2.8.1

Bumps [coverlet.msbuild](https://github.com/tonerdo/coverlet) from 2.3.1 to 2.8.1.
- [Release notes](https://github.com/tonerdo/coverlet/releases)
- [Commits](https://github.com/tonerdo/coverlet/commits)

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

Author: dependabot-preview[bot]

test/json-ld.net.tests/json-ld.net.tests.csproj

@@ -20,7 +20,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="coverlet.msbuild" Version="2.3.1" />
+    <PackageReference Include="coverlet.msbuild" Version="2.8.1" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.5.0" />
     <PackageReference Include="xunit" Version="2.3.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.1" />