Explicitly install @changesets/cli as it's required for the changesets/action action

[gr2m]

We cannot add @changesets/cli as dependency because it conflicts with primer-changesets-cli

This is required for primer/react#3352

[joshblack]

Sorry for the delay on this @gr2m!

Just wanted to double check since this is a shared action, will this impact any projects that are using different versions of the changeset cli package? (older or newer)

What would the process be if downstream teams would like to update to newer versions of this package?

[gr2m]

Good question. There is a theoretical chance that things might break, but

1. the @changesets/cli version had no breaking changes for 4 years
2. Even if a breaking change occurs, I think it's unlikely that the format of the .changesets/*.md files change. That means we don't need to update the workflow file even when repositories start using a new @changesets/cli version
3. If there is a breaking change to the format of the changesets file, we will have to update the line and also update primer-changesets-cli