fix(trtexec_vendor): support build with tensorrt 8.6

[wep21]

Description

🤖 Generated by Copilot at f3ad26f

Refactor the CMake file for trtexec_vendor to make it more readable and maintainable. Use variables for the tensorrt version and remove unnecessary syntax.

Tests performed

Not applicable.

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[yukke42]

LGTM
I have checked with the command trtexec --onnx=(ros2 pkg prefix tensorrt_yolox --share)/data/yolox-tiny.onnx.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.75 ⚠️

Comparison is base (b33d4bb) 13.14% compared to head (f3ad26f) 12.40%.

❗ Current head f3ad26f differs from pull request most recent head 2c05f70. Consider uploading reports for the commit 2c05f70 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3321      +/-   ##
==========================================
- Coverage   13.14%   12.40%   -0.75%     
==========================================
  Files        1278     1368      +90     
  Lines       90746    96191    +5445     
  Branches    27971    27724     -247     
==========================================
+ Hits        11928    11930       +2     
- Misses      66150    71594    +5444     
+ Partials    12668    12667       -1     

Flag	Coverage Δ		*Carryforward flag
differential	∅ <ø> (?)
total	12.40% <ø> (-0.75%)	⬇️	Carriedforward from 1ca02e1

*This pull request uses carry forward flags. Click here to find out more.

see 129 files with indirect coverage changes

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