Fix pybind11 compilation on focal/clang12 combination

[mjcarroll]

Signed-off-by: Michael Carroll michael@openrobotics.org

[codecov]

Codecov Report

Merging #400 (0a9c877) into main (ed2300a) will not change coverage.
The diff coverage is n/a.

❗ Current head 0a9c877 differs from pull request most recent head de356a5. Consider uploading reports for the commit de356a5 to get more accurate results

@@           Coverage Diff           @@
##             main     #400   +/-   ##
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  Coverage   99.90%   99.90%           
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  Files          46       46           
  Lines        4260     4260           
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  Hits         4256     4256           
  Misses          4        4           

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[scpeters]

CI failures on Jammy seem unrelated. I've ticketed them in #401, and I personally am suspicious of gazebosim/gz-cmake#218

[scpeters]

there is an unrelated cmake warning that already exists on main:

• https://build.osrfoundation.org/view/ign-garden/job/ignition_math-ci-main-focal-amd64/25/cmake/

-- Searching for Python - not found.
CMake Warning at /usr/share/cmake/ignition-cmake3/cmake3/IgnConfigureBuild.cmake:55 (message):
   CONFIGURATION WARNINGS:
   -- Python is missing: Python interfaces are disabled.
Call Stack (most recent call first):
  CMakeLists.txt:106 (ign_configure_build)