Fix _sdl_event_watcher cdef #1331

Job	Run time
mypy	26s
sdist	1m 1s
ruff	9s
parse_sdl (macos-latest, 3.2.16)	24s
parse_sdl (windows-latest, 3.2.16)	39s
test-docs	1m 53s
tox (ubuntu-latest)	3m 0s
linux-wheels (x86_64, pp310-manylinux*)	3m 34s
build-macos (pp310-*)	4m 25s
pyodide	2m 40s
build-macos (cp310-*_universal2)	2m 4s
linux-wheels (x86_64, cp310-manylinux*)	4m 11s
build (ubuntu-latest, pypy-3.10, x64)	2m 58s
build (windows-latest, 3.10, x86)	4m 7s
linux-wheels (aarch64, pp310-manylinux*)	3m 35s
linux-wheels (aarch64, cp310-manylinux*)	4m 6s
build (ubuntu-latest, 3.10, x64)	3m 47s
build (windows-latest, 3.10, x64)	2m 58s
build (windows-latest, pypy-3.10, x64)	4m 7s
publish	0s
	50m 4s

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