ci(session-e2e): allow -fms-extensions cgo flag for Windows build

pkg/apm/webrtc adds -fms-extensions to #cgo windows CXXFLAGS; Go's cgo flag
allowlist rejects it unless CGO_CXXFLAGS_ALLOW permits it, matching what
.goreleaser.yaml already does for Windows. test.yaml dodged this by excluding
Windows from its matrix.

Author: u9g

.github/workflows/session-e2e.yaml

@@ -80,6 +80,10 @@ jobs:
 
       - name: Run session e2e
         env:
+          # pkg/apm/webrtc puts -fms-extensions in its #cgo windows CXXFLAGS;
+          # Go's cgo flag allowlist rejects it unless explicitly permitted (same
+          # as .goreleaser.yaml's Windows builds). No-op on Linux/macOS.
+          CGO_CXXFLAGS_ALLOW: -fms-extensions
           LIVEKIT_API_KEY: ${{ secrets.LIVEKIT_API_KEY }}
           LIVEKIT_API_SECRET: ${{ secrets.LIVEKIT_API_SECRET }}
           LIVEKIT_URL: ${{ secrets.LIVEKIT_URL }}