[cmake] Use new mode to find python for pybind11

[BetsyMcPhail]

Update pybind11-config.cmake to follow the same logic as upstream pybind11Common so that the new (not deprecated) method of finding Python is used.

Towards #22009

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This change is 

[BetsyMcPhail]

Experimental packaging (to use to test d-e-e): https://drake-jenkins.csail.mit.edu/view/Packaging/job/mac-arm-sonoma-unprovisioned-clang-cmake-experimental-packaging/3/

Reviewable status: needs platform reviewer assigned, needs at least two assigned reviewers, missing label for release notes (waiting on @BetsyMcPhail)

[BetsyMcPhail]

In the output from the failing Mac d-e-e job (https://github.com/RobotLocomotion/drake-external-examples/actions/runs/11273554281/job/31350829452) we can see a deprecation warning:

CMake Warning (dev) at /opt/drake/lib/cmake/pybind11/FindPythonLibsNew.cmake:101 (message):
  Policy CMP0148 is not set: The FindPythonInterp and FindPythonLibs modules
  are removed.  Run "cmake --help-policy CMP0148" for policy details.  Use
  the cmake_policy command to set the policy and suppress this warning, or
  preferably upgrade to using FindPython, either by calling it explicitly
  before pybind11, or by setting PYBIND11_FINDPYTHON ON before pybind11.

Also, the python that pybind11 is finding using the old, deprecated method is Python 3.9 rather than 3.12, as expected:

-- Found PythonInterp: /usr/bin/python3 (found suitable version "3.9.6", minimum required is "3.6")
-- Found PythonLibs: /Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.9/lib/libpython3.9.dylib

With the changes in this PR, we should no longer see a warning and the mac d-e-e job should pass.

To test, I created an experimental package: https://drake-jenkins.csail.mit.edu/view/Packaging/job/mac-arm-sonoma-unprovisioned-clang-cmake-experimental-packaging/5/

And temporarily updated d-e-e to use that package: RobotLocomotion/drake-external-examples#324.

Reviewable status: needs platform reviewer assigned, needs at least two assigned reviewers, missing label for release notes (waiting on @BetsyMcPhail)

[BetsyMcPhail]

+@sammy-tri for platform review per schedule please. I'm not sure if we also need a feature reviewer for this one?

Reviewable status: LGTM missing from assignee sammy-tri(platform), needs at least two assigned reviewers, missing label for release notes (waiting on @BetsyMcPhail)

[jwnimmer-tri]

I can just take this one to unload -@sammy-tri.

both +(status: single reviewer ok) +(release notes: fix).

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: needs platform reviewer assigned, needs at least one assigned reviewer (waiting on @BetsyMcPhail)