Disable RuntimeAsync in CI to work around .NET 10 test host hang

xUnit v3 test host hangs intermittently on .NET 10 when RuntimeAsync is
enabled (the default). The hang occurs after all tests have passed, with
the test host process stalling indefinitely. Setting DOTNET_RuntimeAsync=0
reliably prevents the hang.

This is a temporary workaround pending a fix in the .NET runtime.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: ericstj

.github/workflows/ci-build-test.yml

@@ -61,6 +61,11 @@ jobs:
       run: make build CONFIGURATION=${{ matrix.configuration }}
 
     - name: 🧪 Test
+      # TODO: Remove DOTNET_RuntimeAsync=0 workaround once the .NET runtime fix is available.
+      # Tracked by: https://github.com/dotnet/runtime/issues/126325
+      # xUnit v3 test host hangs intermittently on .NET 10 with RuntimeAsync enabled.
+      env:
+        DOTNET_RuntimeAsync: "0"
       run: make test CONFIGURATION=${{ matrix.configuration }}
 
     - name: 🧪 AOT Compatibility