check.gst-plugins-good.elements_splitmux.test_splitmuxsink: Sometimes times out in valgrind

See https://gitlab.freedesktop.org/ndufresne/gstreamer/-/jobs/434606

G_DEBUG='gc-friendly' GST_STATE_IGNORE_ELEMENTS='aasink autoaudiosrc autoaudiosink autovideosrc
 autovideosink cacasink cairotextoverlay gtkglsink gtksink jackaudiosrc
 jackaudiosink osssrc osssink osxaudiosink osxaudiosrc osxvideosrc osxvideosink
 pulsesink pulsesrc pulsemixer v4l2src' GST_CHECKS='test_splitmuxsink' GST_PLUGIN_LOADING_WHITELIST='gstreamer:gst-plugins-base:gst-plugins-good@/builds/ndufresne/gstreamer/gst-build/build' CK_TIMEOUT_MULTIPLIER='20' G_SLICE='always-malloc' GST_REGISTRY='/builds/ndufresne/gstreamer/gst-build/build/subprojects/gst-plugins-good/tests/check/elements_splitmux.registry' GST_PLUGIN_PATH_1_0='/builds/ndufresne/gstreamer/gst-build/build' GST_VALIDATE_CONFIG='/builds/ndufresne/gstreamer/gst-build/subprojects/gst-devtools/validate/data/valgrind.config' CK_DEFAULT_TIMEOUT='20' GST_PLUGIN_SYSTEM_PATH_1_0='' ORC_CODE='backup' valgrind --trace-children=yes --tool=memcheck --leak-check=full --leak-resolution=high --errors-for-leak-kinds=definite,indirect --show-leak-kinds=definite,indirect --show-possibly-lost=no --num-callers=20 --error-exitcode=20 --gen-suppressions=all --log-file=/builds/ndufresne/gstreamer/validate-logs/check/gst-plugins-good/elements_splitmux/test_splitmuxsink.valgrind --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gst-devtools/validate/data/gstvalidate.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gstreamer/tests/check/gstreamer.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gst-plugins-base/tests/check/gst-plugins-base.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gst-plugins-good/tests/check/gst-plugins-good.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gst-plugins-bad/tests/check/gst-plugins-bad.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gst-plugins-ugly/tests/check/gst-plugins-ugly.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gst-libav/tests/check/gst-libav.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gst-devtools/validate/data/gstvalidate.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/libnice/tests/libnice.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/libsoup/tests/libsoup.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/glib/glib.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gst-python/testsuite/gstpython.supp --suppressions=/builds/ndufresne/gstreamer/gst-build/subprojects/gst-python/testsuite/python.supp /builds/ndufresne/gstreamer/gst-build/build/subprojects/gst-plugins-good/tests/check/elements_splitmux

elements_splitmux output

Running suite(s): splitmux
0%: Checks: 1, Failures: 0, Errors: 1
../subprojects/gst-plugins-good/tests/check/elements/splitmux.c:228:E:general:test_splitmuxsink:0: (after this point) Test timeout expired
Check suite splitmux ran in 400.063s (tests failed: 1)

CC @thaytan. I think this is a new one.