Bump nunit from 3.11.0 to 3.12.0

Bumps [nunit](https://github.com/nunit/nunit) from 3.11.0 to 3.12.0.
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/master/CHANGES.md)
- [Commits](nunit/nunit@v3.11...v3.12)

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

Author: dependabot-support

System.IO.Abstractions.TestingHelpers.Tests/System.IO.Abstractions.TestingHelpers.Tests.csproj

@@ -46,7 +46,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="nunit" Version="3.11.0" />
+    <PackageReference Include="nunit" Version="3.12.0" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.13.0" />
   </ItemGroup>