fix(clang-tidy): re-enable bugprone-unused-local-non-trivial-variable

[vish0012]

Re-enables bugprone-unused-local-non-trivial-variable in .clang-tidy-ci.

The check was suppressed in #12431 with 2 reported errors. This PR fixes both.

Refs #12450

Fixes

autoware_manual_lane_change_handler

shift_unavailable_reason was computed but never used. Added it to the existing RCLCPP_INFO_STREAM log so the message now reports why the shift was unavailable.

autoware_behavior_path_side_shift_module

centerline_path in scene.cpp was computed but never used anywhere in the package. Removed the dead call.

How to reproduce

colcon build --packages-up-to \
  autoware_manual_lane_change_handler \
  autoware_behavior_path_side_shift_module \
  --cmake-args -DCMAKE_EXPORT_COMPILE_COMMANDS=1

run-clang-tidy -p build/ \
  -export-fixes /tmp/clang-tidy-result/fixes.yaml \
  -j $(nproc) \
  autoware_manual_lane_change_handler \
  autoware_behavior_path_side_shift_module \
  > /tmp/clang-tidy-result/report.log

grep "bugprone-unused-local-non-trivial-variable" /tmp/clang-tidy-result/report.log | grep "error:"

Result

Before: 2 errors
After: 0 errors

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