More gracious errors on TPAC reg page

[samuelweiler]

Describe the issue

When an unaffiliated user tries to register for TPAC, instead of being told "you're not eligible to attend TPAC. If you think you are, here's how to sort that out", they get a 403 Forbidden error, specifically:

"Access Denied The server returned a "403 - Forbidden" error. You do not have sufficient privileges to access the page that you requested..."

To reproduce

Logged in as a test user, load https://www.w3.org/register/tpac2023/form

Expected behavior

I want a gracious error message that tells people how to address the issue.

Screenshots

Additional context Add any other context about the problem here.

[jean-gui]

The message is now more informative:

[samuelweiler]

@jean-gui Thank you!