bump NUnit.Analyzers up to 4.9.1

Author: smdn

src/Smdn.MSBuild.ProjectAssets.Library/project/CodeAnalysis.NUnitAnalyzers.props

@@ -4,7 +4,7 @@ SPDX-License-Identifier: MIT
 -->
 <Project>
   <ItemGroup Label="NUnit Analyzers code analysis">
-    <PackageReference Include="NUnit.Analyzers" Version="4.4.0">
+    <PackageReference Include="NUnit.Analyzers" Version="4.9.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
     </PackageReference>