Add missing break (in unused postsolve code)

[fwesselm]

Added missing break statement.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.80%. Comparing base (0e8db55) to head (97e2caa).
⚠️ Report is 8 commits behind head on latest.

Files with missing lines	Patch %	Lines
highs/presolve/HighsPostsolveStack.h	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           latest    #3020   +/-   ##
=======================================
  Coverage   72.80%   72.80%           
=======================================
  Files         417      417           
  Lines      102156   102150    -6     
  Branches    16467    16464    -3     
=======================================
- Hits        74374    74372    -2     
+ Misses      27506    27502    -4     
  Partials      276      276           

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