DEV: Retry installation of ember exam (PR #14911)

Ember CLI Deploys previously broke because yarn was not run before compiling assets.


Having yarn run inside the rake task was causing us issues previously - that’s why we removed it in DEV: Remove `yarn install` during `assets:precompile` (#14166) · discourse/discourse@0aa8798 · GitHub

We then added a yarn install to web.template.yml: FIX: `yarn install` in web.template.yml (#565) · discourse/discourse_docker@ef5b6e3 · GitHub

If there was an issue, maybe it’s something we need to fix in our internal build templates? (not all of them lean on web.template.yml)

Ah crap @davidtaylorhq - locally at least it doesn’t work UNLESS it’s a dev dependency.

Let’s try by putting it in both areas. I think that might get it to install properly.