test(CI): Have GitHub use npm ci instead of npm install

[cpcallen]

The basics

• I validated my changes

The details

Proposed Changes

Have the GitHub build workflow, which runs our tests, use npm ci instead of npm install when installing dependencies.

Reason for Changes

This should help ensure that CI catches PRs that update package.json without updating package-lock.json to match.

Additional Information

Proposed in response to breakage caused by PR #8209.

[cpcallen]

OK the build workflow failed as desired at commit e01154c (upon which I created this branch) since package-lock.json is indeed mismatched against package.json at this point. Going to rebase this on the parent commit (which is not broken) to verify it passes there.

[cpcallen]

OK, rebasing this onto a known-good commit did not cause tests to start passing, because it turns out that the checkout workflow checks out a commit that's a merge commit merging the PR into develop, not the tip-of-PR-branch commit. TIL.

Not sure when that changed but obviously it's a lot better because it tells you if your PR will break develop when committed, not just whether it passes tests in isloation.