Correct path in register_update_item docstring

[bmcandr]

Description:

The docstring for the transaction extension's register_update_item function lists an incomplete path:

(PUT /collections/{collection_id}/items)

vs

"/collections/{collection_id}/items/{item_id}"

PR Checklist:

• Code is formatted and linted (run pre-commit run --all-files)
• Tests pass (run make test)
• Documentation has been updated to reflect changes, if applicable, and docs build successfully (run make docs)
• Changes are added to the CHANGELOG.

[geospatial-jeff]

Thanks @bmcandr!