Bump NUnit from 4.6.0 to 4.6.1 (#451)

Updated [NUnit](https://github.com/nunit/nunit) from 4.6.0 to 4.6.1.

<details>
<summary>Release notes</summary>

_Sourced from [NUnit's
releases](https://github.com/nunit/nunit/releases)._

## 4.6.1

See [release
notes](https://docs.nunit.org/articles/nunit/release-notes/framework.html#nunit-461---may-18-2026)
for details.

Commits viewable in [compare
view](nunit/nunit@v4.6.0...v4.6.1).
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Directory.Packages.props

@@ -19,7 +19,7 @@
     <PackageVersion Include="System.CommandLine.DragonFruit" Version="0.4.0-alpha.25320.106" />
     <!-- Reference-only packages for test framework namespace resolution in analyzer tests -->
     <PackageVersion Include="xunit.v3.core" Version="3.2.2" />
-    <PackageVersion Include="NUnit" Version="4.6.0" />
+    <PackageVersion Include="NUnit" Version="4.6.1" />
     <PackageVersion Include="TUnit.Core" Version="1.45.8" />
   </ItemGroup>
 </Project>