fix 3d.pyi install (followup da317dd8dea0)

[jef-n]

$ find build -name "*3d*.pyi"
build/python/3d/build/_3d_p/_3d_p.pyi

From the nightlies:

-- Installing: /build/qgis-3.39.0+git20240903+b53968c771e+36jammy/debian/tmp/usr/lib/python3/dist-packages/qgis/_gui.so
-- Set runtime path of "/build/qgis-3.39.0+git20240903+b53968c771e+36jammy/debian/tmp/usr/lib/python3/dist-packages/qgis/_gui.so" to ""
CMake Error at python/cmake_install.cmake:134 (file):
  file INSTALL cannot find
  "/build/qgis-3.39.0+git20240903+b53968c771e+36jammy/debian/build/python/3d/build/3d_p/3d_p.pyi":
  No such file or directory.
Call Stack (most recent call first):
  cmake_install.cmake:69 (include)

[github-actions]

🪟 Windows builds ready!

Windows builds of this PR are available for testing here. Debug symbols for this build are available here.

(Built from commit d281342)

[jgrocha]

Hi @jef-n

On my build, I don't get the _3d_p.pyi and so this PR breaks my sudo cmake --build . --target install.

I wrote the details on #58534 (comment)

What is different in my setup?

[nyalldawson]

@jgrocha what version of sip are you using?

[nirvn]

I have the same issue, using sip 4.

[jgrocha]

@jgrocha what version of sip are you using?

4.19.25

[jgrocha]

Ping @jef-n

Is there anything we can do about this? Can we add an additional condition to python/CMakeLists.txt to both 3d_p.pyi and _3d_p.pyi?