build: restore build:packages on turbo 2.10.1+

[arbrandes]

Description

make build-packages fails on turbo 2.10.1 and later with package_task_in_single_package_mode, rejecting the //#dev:site root task. turbo 2.10.1 reworked package manager detection, and with no packageManager field it falls back to single-package mode, where //# root tasks are invalid.

Declaring packageManager fixes it. The --dangerously-disable-package-manager-check flag was compensating for the missing field and is what now triggers the fallback, so it comes out too. The lockfile bump takes turbo to an affected version, where this is verified.

Part of openedx/frontend-base#312.

LLM usage notice

Built with assistance from Claude.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.64%. Comparing base (d7861e6) to head (2547abf).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1689   +/-   ##
=======================================
  Coverage   93.64%   93.64%           
=======================================
  Files          94       94           
  Lines        2076     2076           
  Branches      603      592   -11     
=======================================
  Hits         1944     1944           
  Misses        129      129           
  Partials        3        3           

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