Potential fix for code scanning alert no. 5430: Comparison result is always the same

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: bigfooted

SU2_CFD/src/solvers/CSolver.cpp

@@ -3598,7 +3598,7 @@ void CSolver::LoadInletProfile(CGeometry **geometry,
 
   /*--- strip the .dat (or other) extension from the inlet_profile.dat filename. ---*/
 
-  unsigned short lastindex = profile_filename.find_last_of('.');
+  std::string::size_type lastindex = profile_filename.find_last_of('.');
   string ext = "";
 
   /*--- Get the extension, including the dot. ---*/