[github-maintenance] Fix pnpm-workspace.yaml configuration

[marimo-github-maintenance-bot]

Fixes misconfigured fields in pnpm-workspace.yaml.

See the tracking issue in github-maintenance.

[kirangadhave]

Closing in favor of #30, which takes the Renovate-side half of this (a 7-day minimumReleaseAge so no release younger than a week is ever proposed).

The pnpm-side floor here is the stronger protection and worth keeping, but this branch cannot land as-is:

• minimumReleaseAge: 20160 (14 days) fails resolution today. Four package.json floors point at releases younger than that, and no older version satisfies their caret ranges, so a fresh lockfile errors with ERR_PNPM_NO_MATURE_MATCHING_VERSION (349 versions). This is what the red CI on this PR is: ERR_PNPM_LOCKFILE_RESOLUTION_VERIFICATION, 83 entries. I reproduced it locally at 7 days too.
• onlyBuiltDependencies: [] re-adds the pre-pnpm-11 key alongside the allowBuilds block already in the file. Redundant at best, and it may override esbuild: true, which the extension build needs.

Plan is to re-add the good parts (minimumReleaseAge, blockExoticSubdeps, trustPolicy: no-downgrade) deliberately on or after 2026-08-03, once those floors mature. By then #30 keeps Renovate from proposing anything under 7 days, so the two policies stay consistent.