Fix licensing of pnpm-workspace

Every time Renovate Bot applies changes to the pnpm-workspace.yaml it wipes out the licensing comments and the document-start. This causes unnecessary manual fixing work for relevant Renovate MR's.

• pnpm-workspace.yaml should be licensed via Reuse
• relax doc-start rule for the pnpm-workspace.yaml

Seems to be the same root cause https://github.com/renovatebot/renovate/discussions/41756