With changes in this PR, now all tests pass on macOS and Windows. In Linux CI, following tests fail:

	509 - test/grdfill/gridfill.sh (Failed)
	521 - test/grdgdal/gdal_nn.sh (Failed)
	552 - test/grdimage/image_vartrans.sh (Failed)
	647 - test/grdvector/shrink.sh (Failed)
	702 - test/mapproject/proj4.sh (Failed)
	738 - test/nearneighbor/nat_nn.sh (Failed)
	754 - test/potential/firmoviscous.sh (Timeout)
	755 - test/potential/firmoviscous2.sh (Timeout)

Not sure why firmoviscous tests timeout in CI. They work well for me locally.

Do the other tests fail for you as well on Linux?

The *_nn.sh failures are extremely irritating for me. I spent awful long time figuring out why originally they failed and it turned out to be a GDAL version issue. Since ~2 years(?) now we have a test on GDAL version to that, but it insists in failing under Linux.

And why is proj4.sh failing?

better to merge this PR first so that I can look into the details of the failing tests.

With changes in this PR, now all tests pass on macOS and Windows. In Linux CI, following tests fail:

	509 - test/grdfill/gridfill.sh (Failed)
	521 - test/grdgdal/gdal_nn.sh (Failed)
	552 - test/grdimage/image_vartrans.sh (Failed)
	647 - test/grdvector/shrink.sh (Failed)
	702 - test/mapproject/proj4.sh (Failed)
	738 - test/nearneighbor/nat_nn.sh (Failed)
	754 - test/potential/firmoviscous.sh (Timeout)
	755 - test/potential/firmoviscous2.sh (Timeout)

Not sure why firmoviscous tests timeout in CI. They work well for me locally.

I have gridfill.sh, image_vartrans.sh and shrink.sh failing for me on Linux, and all other tests pass.

I have GDAL 3.7.3 installed and the Linux CI has GDAL 3.4.1.

The *_nn.sh fail with up-down flip. Left is the correct one and right is the wrong one.

I have GDAL 3.7.3 installed and the Linux CI has GDAL 3.4.1.

... typical of Ubuntu

I have a vague recall that the condition to workaround the GDAL issue was for GDAL 3.5.0