fix(autoware_freespace_planning_algorithms): fix bugprone-errors

[kobayu858]

Description

This is a fix based on clang-tidy bugprone-signed-char-misuse and bugprone-integer-division error.

/home/emb4/autoware/autoware/src/universe/autoware.universe/planning/autoware_freespace_planning_algorithms/src/abstract_algorithm.cpp:118:22: error: 'signed char' to 'const int' conversion; consider casting to 'unsigned char' first. [bugprone-signed-char-misuse,-warnings-as-errors]
    const int cost = costmap_.data[i];
                     ^

/home/emb4/autoware/autoware/src/universe/autoware.universe/planning/autoware_freespace_planning_algorithms/src/astar_search.cpp:391:11: error: result of integer division used in a floating point context; possible loss of precision [bugprone-integer-division,-warnings-as-errors]
         (abs(steering_index) / planner_common_param_.turning_steps);
          ^

Related links

Parent Issue:

• Link

How was this PR tested?

Notes for reviewers

None.

Interface changes

None.

Effects on system behavior

None.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.83%. Comparing base (b9ebc42) to head (523f650).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9670      +/-   ##
==========================================
- Coverage   29.83%   29.83%   -0.01%     
==========================================
  Files        1443     1449       +6     
  Lines      108599   108640      +41     
  Branches    42667    42666       -1     
==========================================
+ Hits        32405    32409       +4     
- Misses      73011    73049      +38     
+ Partials     3183     3182       -1     

Flag	Coverage Δ		*Carryforward flag
differential	24.49% <100.00%> (?)
total	29.83% <ø> (-0.01%)	⬇️	Carriedforward from b9ebc42

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