v0.29: Changes to `invalid_geo_field` error

[guimachiavelli]

The invalid_geo_field error has two new variant messages: one when _geo exists but is not an object, and another when _geo exists and is an object, but is missing both _geo.lat and _geo.lng fields.

This error is already present in the docs, but we can update the text slightly to reflect new information.

References

• issue: Add new error code: invalid_geo_field meilisearch#2707
• spec: Geosearch - Add error variants for invalid_geo_field error specifications#161
• SME: @Kerollmops