Fix HostingListener memory leak from static AsyncLocal

[Copilot]

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Fix memory leak in WebApplicationTests HostingListener

Description

HostingListener._currentListener was declared as static readonly AsyncLocal<HostingListener>, causing the static AsyncLocal instance to retain references to HostingListener instances beyond their disposal, preventing garbage collection.

Changes:

• Made _currentListener an instance field instead of static (one-line change)

The instance-level AsyncLocal correctly scopes to each listener and gets collected with its owner. The check if (_currentListener.Value != this) remains functionally correct as each instance now validates against its own AsyncLocal.

Note: This fix applies to internal test-only code. The production code fix is tracked in dotnet/runtime#124391.

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[halter73]

I forgot the real code for this is in the runtime repo, and we only use the AsyncLocal modified by this PR for our own internal tests. The real PR to fix this is now at dotnet/runtime#124391.

There's no reason not to fix this for our own internal usage, but I don't think we need to test our internal-test-only code. @copilot Can you remove the HostingListener_DoesNotLeakMemory test? This PR should just be a one-line change removing the static keyword.

[Copilot]

I forgot the real code for this is in the runtime repo, and we only use the AsyncLocal modified by this PR for our own internal tests. The real PR to fix this is now at https://github.com/dotnet/runti...

Removed the test. The PR now contains only the one-line change removing the static keyword (commit a08916f).

[Copilot]

Pull request overview

This PR addresses a memory retention issue in the DefaultBuilder test infrastructure by avoiding a static AsyncLocal that could keep HostingListener instances alive longer than intended.

Changes:

• Changed HostingListener._currentListener from a static readonly AsyncLocal<HostingListener> to an instance readonly AsyncLocal<HostingListener>.

[halter73]

I'm going to close this based on the discussion at dotnet/runtime#124391 (comment)