chore/update yarn

[bdb-dd]

Update yarn to v4.3.1
Downgrade eslint to v8 since many third party packages have not yet upgraded to v9

Was not able to fix the non-overlapping zod related deps, seems to be an inconsistency in the referenced versions from @instructor-ai/instructor@1.5.0:

Package @digdir/assistant-slack-app@workspace:apps/slack-app is requested to provide zod by its descendants

@digdir/assistant-slack-app@workspace:apps/slack-app
├─ @instructor-ai/instructor@npm:1.5.0 [678a4] (via >=3.22.4)
│  ├─ zod-stream@npm:1.0.3 [64e0d] (via >=3.22.4)
│  │  ├─ schema-stream@npm:3.1.0 [860df] (via 3.22.4)
│  │  └─ zod-to-json-schema@npm:3.23.0 [860df] (via ^3.23.3)
│  └─ zod-validation-error@npm:2.1.0 [64e0d] (via ^3.18.0)
└─ zod-to-json-schema@npm:3.23.1 [678a4] (via ^3.23.3)