Don't use ament_export_targets from package sub folder (backport #1889)

[mergify]

This is an automatic backport of pull request #1889 done by Mergify.
Cherry-pick of da0b248 has failed:

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	both modified:   moveit_core/CMakeLists.txt

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Cherry-pick of acda563 has failed:

On branch mergify/bp/humble/pr-1889
Your branch is ahead of 'origin/humble' by 1 commit.
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	modified:   moveit_core/CMakeLists.txt

Unmerged paths:
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	both modified:   moveit_core/collision_detection_bullet/CMakeLists.txt

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[henningkayser]

@tylerjw would you have time to address the conflicts?

[tylerjw]

Fixed up this backport and tested locally. I'll merge if CI passes.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01% ⚠️

Comparison is base (a1789ff) 50.95% compared to head (59dcbc7) 50.94%.

Additional details and impacted files

@@            Coverage Diff             @@
##           humble    #1893      +/-   ##
==========================================
- Coverage   50.95%   50.94%   -0.01%     
==========================================
  Files         382      382              
  Lines       31889    31889              
==========================================
- Hits        16246    16242       -4     
- Misses      15643    15647       +4     

see 1 file with indirect coverage changes

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