CI: Fix 404 on CI link testing

[markmandel]

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking
/kind bug

/kind cleanup

/kind documentation
/kind feature
/kind hotfix
/kind release

What this PR does / Why we need it:

Not sure why, but youtube playlist links are 404ing.

I couldn't specify data-proofer-ignore since it's part of the Docsy layout, so I ignored it at the htmltest layer.

Did some minor cleanup while I was in there as well - updating some yaml formatting and updating the User-Agent as well.

Which issue(s) this PR fixes:

Unblocks CI

Special notes for your reviewer:

N/A

[agones-bot]

Build Succeeded 👏

Build Id: d98dab3c-8504-40d5-a40a-51cb9deb0f8a

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.37.0-dev-9b2c1e5-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.37.0-dev-9b2c1e5-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.37.0-dev-9b2c1e5-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.37.0-dev-9b2c1e5-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.37.0-dev-9b2c1e5-amd64
• Linux C++ SDK (build): agonessdk-1.37.0-dev-9b2c1e5-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.37.0-dev-9b2c1e5-amd64.zip

A preview of the website (the last 30 builds are retained):

• https://9b2c1e5-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3542/head:pr_3542 && git checkout pr_3542
• helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.37.0-dev-9b2c1e5-amd64