x/pkgsite: get the builders green

[matloob]

This issue is for getting the builders for x/pkgsite passing.

[findleyr]

Kokoro currently sets the TryBot-Result label. I think we need to solve that ownership model first.

[hyangah]

Is it a duplicate of #59347 or a subtask of it?

[matloob]

I think this is a subtask.

[gopherbot]

Change https://go.dev/cl/508655 mentions this issue: dashboard: disable pkgsite on misc-compile-aix-ppc64 builder

[gopherbot]

Change https://go.dev/cl/508864 mentions this issue: dashboard: disable pkgsite on plan9 builders

[gopherbot]

Change https://go.dev/cl/509475 mentions this issue: dashboard: stop building packagesite on aix and plan9 misc-compile