Report MTP test results as GitHub Actions annotations

CI has been failing on real integration tests (Slack API calls timing
out) but the raw dotnet test console output makes it hard to see which
test actually failed. Add Microsoft.Testing.Extensions.GitHubActionsReport
and pass --report-gh through the Bullseye test target so Microsoft.Testing.Platform
writes a per-assembly pass/fail summary with collapsible failure details
to the GitHub Actions job summary. No-ops outside GITHUB_ACTIONS, so
local runs are unaffected.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: johnkors

build/Program.cs

@@ -15,7 +15,7 @@
 
 Target(Build, new[] { Restore }, () => RunAsync("dotnet", $"build {solution} --no-restore"));
 
-Target(Test, new[] { Build }, () => RunAsync("dotnet", $"test {solution} --no-build"));
+Target(Test, new[] { Build }, () => RunAsync("dotnet", $"test {solution} --no-build -- --report-gh"));
 
 Target(Pack, new[] { Build }, async () =>
 {

source/test/Slackbot.Net.SlackClients.Http.Tests/Slackbot.Net.SlackClients.Http.Tests.csproj

@@ -17,6 +17,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.10.0"/>
     <PackageReference Include="xunit.v3" Version="4.0.0"/>
     <PackageReference Include="xunit.runner.visualstudio" Version="4.0.0"/>
+    <PackageReference Include="Microsoft.Testing.Extensions.GitHubActionsReport" Version="2.4.0"/>
   </ItemGroup>
 
   <ItemGroup>