fix: unit preview in course outline sidebar

[navinkarkera]

Description

Clicking on Preview tab of unit sidebar in course outline crashes due to use of useUnitSidebarContext without provider.

This PR fixes it by making the provider optional based on readOnly flag.

Useful information to include:

• Which user roles will this change impact?: "Course Author",

Supporting information

• Probably introduced in feat: Unit align sidebar [FC-0114] #2856
• Private-ref: https://tasks.opencraft.com/browse/FAL-4324

Testing instructions

• Verify that preview tab in unit sidebar in course outline works.

Other information

Include anything else that will help reviewers and consumers understand the change.

• Does this change depend on other changes elsewhere?
• Any special concerns or limitations? For example: deprecations, migrations, security, or accessibility.

Best Practices Checklist

We're trying to move away from some deprecated patterns in this codebase. Please
check if your PR meets these recommendations before asking for a review:

• Any new files are using TypeScript (.ts, .tsx).
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• Use React Query to load data from REST APIs. See any apiHooks.ts in this repo for examples.
• All new i18n messages in messages.ts files have a description for translators to use.
• Avoid using ../ in import paths. To import from parent folders, use @src, e.g. import { initializeMocks } from '@src/testUtils'; instead of from '../../../../testUtils'

[openedx-webhooks]

Thanks for the pull request, @navinkarkera!

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.51%. Comparing base (24e1c73) to head (23e2b00).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2940   +/-   ##
=======================================
  Coverage   95.51%   95.51%           
=======================================
  Files        1329     1329           
  Lines       30557    30557           
  Branches     6925     6930    +5     
=======================================
  Hits        29186    29186           
  Misses       1303     1303           
  Partials       68       68           

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[rpenido]

LGTM 👍
Thank you for your work, @navinkarkera!

• I tested this using the instructions from the PR
• I read through the code
• I checked for accessibility issues
• Includes documentation

This is ready for you @ChrisChV.

[ChrisChV]

Looks good! Thanks! 👍