Bump the tunit group with 1 update

Bumps TUnit from 1.5.80 to 1.6.20

---
updated-dependencies:
- dependency-name: TUnit
  dependency-version: 1.6.20
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: tunit
...

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

Author: dependabot[bot]

src/Directory.Packages.props

@@ -13,7 +13,7 @@
     <PackageVersion Include="Microsoft.NETCore.App.Ref" Version="9.0.10" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
     <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="8.0.0" />
-    <PackageVersion Include="TUnit" Version="1.5.80" />
+    <PackageVersion Include="TUnit" Version="1.6.20" />
     <PackageVersion Include="Verify.DiffPlex" Version="3.1.2" />
     <PackageVersion Include="Verify.SourceGenerators" Version="2.5.0" />
     <PackageVersion Include="Verify.TUnit" Version="31.9.0" />