Unexpected failure on CI: input_decoder test doesn't flush on seek

See https://code.videolan.org/videolan/vlc/-/jobs/1141951

[00007f117c0020a0] test_input_decoder_mock decoder: Send first frame from decoder to video output
[00007f117c0020a0] main decoder debug: Received first picture
[00007f117c0020a0] test_input_decoder_mock decoder: Wait for the display to prepare the frame
[00007f117c0020a0] test_input_decoder_mock decoder: Trigger decoder and vout flush
[00007f117c0020a0] test_input_decoder_mock decoder: Wait for the picture to be flushed from the vout
[00007f117c0091a0] xdg inhibit warning: error starting xdg-screensaver: No such file or directory
FAIL test_src_input_decoder (exit status: 134)

Normal run:

[00007fd31c002010] test_input_decoder_mock decoder: Send first frame from decoder to video output
[00007fd31c002010] main decoder debug: Received first picture
[00007fd31c002010] test_input_decoder_mock decoder: Wait for the display to prepare the frame
[00007fd31c002010] test_input_decoder_mock decoder: Trigger decoder and vout flush
[00007fd31c002010] test_input_decoder_mock decoder: Wait for the picture to be flushed from the vout
[0000556b6783b620] main input debug: control type=27
[0000556b6783b620] main input debug: control type=2
[0000556b6783b620] main input debug: ES_OUT_RESET_PCR called
[00007fd31c002010] test_input_decoder_mock decoder: Re-queue the picture to the vout before decoder::pf_flush is called
[00007fd31c002010] test_input_decoder_mock decoder: Ensure the picture has been discarded by the input decoder
[00007fd31c002010] test_input_decoder_mock decoder: Nothing to do from pf_decode, let pf_flush be called by the input decoder

Logs seems to point at failure from the test to trigger a flush with vlc_player_SeekByPos, since there is no control triggered in the logs.