docker: Downgrade PDAL to 2.7.1 in ubuntu_wxgui

[echoix]

When building the image, only PROJ 8.2.1 is available, and PDAL 2.7.2 checks for PROJ 9.0+

This is a temporary fix to continue having working Docker builds. Renovate will open a PR to update PDAL again afterwards. But a more substantial fix is needed.