splitmuxsrc: test_splitmuxsrc_caps_change times out

CI log: https://gitlab.freedesktop.org/alatiera/gst-ci/-/jobs/77348

Output:

check.gst-plugins-good.elements_splitmux.test_splitmuxsrc_caps_change: Failed 'Application returned 1'
       You can reproduce with: GST_CHECKS='test_splitmuxsrc_caps_change' GST_STATE_IGNORE_ELEMENTS='aasink autoaudiosrc autoaudiosink autovideosrc
 autovideosink cacasink cairotextoverlay jackaudiosrc jackaudiosink
 osssrc osssink osxaudiosink osxaudiosrc osxvideosrc osxvideosink
 pulsesink pulsesrc pulsemixer v4l2src' GST_PLUGIN_LOADING_WHITELIST='gstreamer:gst-plugins-base:gst-plugins-good@/builds/alatiera/gst-ci/gst-build/build' CK_DEFAULT_TIMEOUT='20' GST_PLUGIN_PATH_1_0='/builds/alatiera/gst-ci/gst-build/build' GST_REGISTRY='/builds/alatiera/gst-ci/gst-build/build/subprojects/gst-plugins-good/tests/check/elements_splitmux.registry' GST_PLUGIN_SYSTEM_PATH_1_0='' /builds/alatiera/gst-ci/gst-build/build/subprojects/gst-plugins-good/tests/check/elements_splitmux

Dumping log files on failure

Dumping contents of /builds/alatiera/gst-ci/validate-output/logs/check/gst-plugins-good/elements_splitmux/test_splitmuxsrc_caps_change

=================
Test name: check.gst-plugins-good.elements_splitmux.test_splitmuxsrc_caps_change
Command: '/builds/alatiera/gst-ci/gst-build/build/subprojects/gst-plugins-good/tests/check/elements_splitmux'
=================

Running suite(s): splitmux
0%: Checks: 1, Failures: 0, Errors: 1
../subprojects/gst-plugins-good/tests/check/elements/splitmux.c:305:E:caps_change:test_splitmuxsrc_caps_change:0: (after this point) Test timeout expired
Check suite splitmux ran in 20.002s (tests failed: 1)