Bump the nuget-packages group with 1 update (#595)

Bumps Verify.TUnit from 31.20.0 to 31.21.0

---
updated-dependencies:
- dependency-name: Verify.TUnit
  dependency-version: 31.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: nuget-packages
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Directory.Packages.props

@@ -32,7 +32,7 @@
     <PackageVersion Include="System.Text.Json" Version="9.0.9" />
     <PackageVersion Include="TUnit" Version="1.58.0" />
     <PackageVersion Include="Verify.SourceGenerators" Version="2.5.0" />
-    <PackageVersion Include="Verify.TUnit" Version="31.20.0" />
+    <PackageVersion Include="Verify.TUnit" Version="31.21.0" />
     <PackageVersion Include="Vortice.Dxc" Version="3.8.3" />
     <PackageVersion Include="Vortice.Mathematics" Version="2.1.1" />
     <PackageVersion Include="Vortice.D3DCompiler" Version="3.8.3" />