Build: Run pretest before test:* npm scripts

Build: Run pretest before test:* npm scripts

Build was already happening in scripts like `test:browser` but those scripts
were missing `pretest`, meaning that running `npm install && npm test:browser`
may have failed if `pretest` wasn't run before or if its results were out of
date.

Even worse, with such stale data some tests may erroneously succeed.

This also removes a separate `pretest` step from GitHub Actions as it's no
longer needed.

Closes gh-5338