feat: fixed loading issue for wrong username

[sundasnoreen12]

INF-1594

Description

I resolved an issue that occurred when navigating to the learner profile of a non-existent user. Previously, the user's page would display a perpetual "loading" spinner, but it now correctly displays the content of the "Not Found" page.

Screenshots/sandbox (optional):

Include a link to the sandbox for design changes or screenshot for before and after. Remove this section if it's not applicable.

Before

After

Merge Checklist

• If your update includes visual changes, have they been reviewed by a designer? Send them a link to the Sandbox, if applicable.
• Is there adequate test coverage for your changes?

Post-merge Checklist

• Deploy the changes to prod after verifying on stage or ask @openedx/2u-infinity to do it.
• 🎉 🙌 Celebrate! Thanks for your contribution.

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 4 lines in your changes missing coverage. Please review.

Project coverage is 66.90%. Comparing base (3270e27) to head (c66face).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/profile/data/sagas.js	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1139      +/-   ##
==========================================
+ Coverage   66.78%   66.90%   +0.11%     
==========================================
  Files          51       51              
  Lines         849      855       +6     
  Branches      175      177       +2     
==========================================
+ Hits          567      572       +5     
  Misses        272      272              
- Partials       10       11       +1     

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