Websocket case-sensitive check of header `Sec-WebSocket-Accept`

Line 107 in websocket.php https://gricad-gitlab.univ-grenoble-alpes.fr/moodle-plugins/moodle-qtype_vplquestion/-/blob/master/classes/websocket.php?ref_type=heads#L107

Uses a case-sensitive regex pattern for the "Sec-WebSocket-Accept" header in order to verify the websocket challenge response. This should be a case-insensitive pattern as headers are themselves case-insensitive.

I have had to fix this locally on our moodle install today as our reverse proxy sets all http header names to lowercase.

Besides this VPL questions is an excellent extension to what VPL itself already provides.