Bump TUnit from 1.5.60 to 1.9.81 (#32)

---
updated-dependencies:
- dependency-name: TUnit
  dependency-version: 1.9.81
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

src/OpenApiSourceGenerator.Tests/OpenApiSourceGenerator.Tests.csproj

@@ -13,7 +13,7 @@
     <PackageReference Include="Microsoft.OpenApi.YamlReader" Version="3.0.2" />
     <PackageReference Include="Reqnroll.TUnit" Version="3.3.1" />
     <PackageReference Include="Shouldly" Version="4.3.0" />
-    <PackageReference Include="TUnit" Version="1.5.60" />
+    <PackageReference Include="TUnit" Version="1.9.81" />
   </ItemGroup>
 
   <ItemGroup>