Fix typo

[DLu]

Description

I fixed a typo in the documentation

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[AdamPettinger]

👍 briefly flicked through the rest of the same file and didn't see any other of these

[codecov]

Codecov Report

Merging #510 (4eee85b) into main (fb94e78) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #510   +/-   ##
=======================================
  Coverage   45.17%   45.17%           
=======================================
  Files         169      169           
  Lines       18734    18734           
=======================================
  Hits         8462     8462           
  Misses      10272    10272           

Impacted Files	Coverage Δ
...del/include/moveit/robot_model/joint_model_group.h	84.00% <ø> (ø)

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