[3.14] gh-143460: Correct unlimited stack size skip for Emscripten (GH-143765) (#143819)

Modifies the test skip for unlimited stack size to add Emscripten to the
exclusion list.
(cherry picked from commit 1857a40807daeae3a1bf5efb682de9c9ae6df845)

Co-authored-by: Russell Keith-Magee <russell@keith-magee.com>