fix bug with bulk ocp lithiation

[rtimms]

Description

Fixes a bug where "lithiation" wasn't passed to the bulk OCP ( U_lith_bulk = self.phase_param.U(sto_bulk, T_bulk, "lithiation")) which led to incorrect outputs for the "particle concentration overpotential" variables.

Fixes # (issue)

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #)

Important checks:

Please confirm the following before marking the PR as ready for review:

• No style issues: nox -s pre-commit
• All tests pass: nox -s tests
• The documentation builds: nox -s doctests
• Code is commented for hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.77%. Comparing base (6ba2cde) to head (2c36b3d).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #5280   +/-   ##
========================================
  Coverage    98.77%   98.77%           
========================================
  Files          321      321           
  Lines        27727    27727           
========================================
  Hits         27387    27387           
  Misses         340      340           

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