Fixes yarn why -R

[arcanis]

What's the problem this PR addresses?

When using the -R flag on a flag with a large amount of workspaces, yarn why may fail to return enough information to answer the question "why is this package here". This is because of a bug in the implementation where we decline to print a package in the tree view if:

• We saw it before, or
• It's a workspace (because we'll print it later anyway)

However we check the first condition first and we put the package in the "seen" list before we check whether it's a workspace. As a result, workspaces that are dependencies of other workspaces won't have their dependencies shown.

How did you fix it?

Flipped the two conditions.

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.

• I will check that all automated PR checks pass before the PR gets reviewed.

[merceyz]

Could you add a test for this?