fix(login): revert provider user ID format

[frgfm]

This PR fixes a typo in the format used for provider_user_id, which was causing a crash on the login route.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 83.35%. Comparing base (4f48666) to head (3724a23).
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/app/api/api_v1/endpoints/login.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #112   +/-   ##
=======================================
  Coverage   83.35%   83.35%           
=======================================
  Files          29       29           
  Lines         883      883           
=======================================
  Hits          736      736           
  Misses        147      147           

Flag	Coverage Δ
unittests	83.35% <50.00%> (ø)

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