Make yarn test fire on pull_request and fix snapshot fail on master

[ChefHutch]

Problem

I noticed that a test was failing on master. It turns out that the push action only seems to run before a branch has been PRed - i.e. - https://github.com/ChefHutch/pancake-toolkit/runs/2295909352 (the first push to this branch before I created the PR).

Once PRed, the action doesn't seem to run. Notice CI passes (with a failing test) for every commit in this PR before I add the on: [... pull_request] value in e4dd4e7 (at which point yarn test fires, and CI fails. Woot!).

Code changes

• Make test action run on pull_request
• Tidy syntax to match other actions
• Update failing snapshot

[Chef-Cheems]

LGTM, thanks!
I wonder if push even necessary. In case you push the branch but decide not to open a PR and abandon the branch - actions ran for nothing.

Seems like other pipelines don't have push at all and doing just fine.