Bump Refit from 6.0.38 to 8.0.0 in /tests

Bumps [Refit](https://github.com/reactiveui/refit) from 6.0.38 to 8.0.0.
- [Release notes](https://github.com/reactiveui/refit/releases)
- [Commits](reactiveui/refit@v6.0.38...8.0.0)

---
updated-dependencies:
- dependency-name: Refit
  dependency-type: direct:production
...

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

tests/ZabbixSender.Async.Tests.csproj

@@ -18,7 +18,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="Refit" Version="6.0.38" />
+    <PackageReference Include="Refit" Version="8.0.0" />
     <PackageReference Include="Refit.HttpClientFactory" Version="6.0.38" />
     <PackageReference Include="Shouldly" Version="3.0.2" />
   </ItemGroup>