Don't run builder GitHub Actions on forks

[chosak]

Currently there are two GitHub Actions for this repository that attempt to gate their execution by ensuring that they don't run on forks, using the check

if: github.repository == 'cfpb/consumerfinance.gov'

This doesn't work properly, because on PRs this still refers to this repo (cfpb/consumerfinance.gov), not the fork.

You can see an example where this didn't work right on #8617, where @lfatty opened a PR from his fork but the "Build cf.gov artifact" action still ran.

This PR attempts to fix the syntax to work properly using this check instead:

if: "! github.event.pull_request.head.repo.fork"

I've created this PR from my fork so these two actions should not run.

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code follows the standards laid out in the CFPB development guidelines