Fix Link Checker issues

[kingdonb]

There are two types of issues I noticed in the link checker output from

• https://github.com/fluxcd/community/actions/runs/31599044321/job/94121562620?pr=475

1. https://github.com/fluxcd/website/blob/main/content/en/support.md - this is referenced in SUPPORT.md and it is a dead link.
2. Wikia and Sched have banned scraping from GitHub Actions and all return a 403 Network Error, or cached Error. They can be excluded from link checker via wildcards. The CNCF events pages all use these platforms historically, so we've got tons of links to them.

Just making a note for later. I will try to follow up on this before #475 closes.