Make HttpStress fail on unobserved exceptions

[antonfirsov]

There were no unobserved exceptions in recent HttpStress runs, so it should be OK (and desired) to fail the test run if we detect one.

[Copilot]

Pull Request Overview

This PR updates the HttpStress test behavior to fail the test run if any unobserved exceptions occur.

• Updated the exit condition to check for both stress errors and unobserved exceptions.
• Added a new log message in PrintUnobservedExceptions to indicate when no unobserved exceptions are detected.

Comments suppressed due to low confidence (1)

src/libraries/System.Net.Http/tests/StressTests/HttpStress/Program.cs:247

• Ensure that s_unobservedExceptions is a thread-safe collection, as its Count property is used in a conditional check which could be subject to race conditions in a concurrent test environment.

return client?.TotalErrorCount == 0 && s_unobservedExceptions.Count == 0 ? ExitCode.Success : ExitCode.StressError;

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

[antonfirsov]

/azp run runtime-libraries stress-http

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[antonfirsov]

/ba-g failures in the runtime pipeline are unrelated