autotest/gcore/pixfun.py: attempt at fixing failure on CI build-linux…

…-ubuntu-focal

Since today, and perhaps related with an update of pypi numpy-1.22
(although that some pull requests aren't affected), we get a failure in
test_pixfun_log10_r().
See https://github.com/OSGeo/gdal/runs/4684162794

autotest/gcore/pixfun.py

@@ -580,7 +580,7 @@ def test_pixfun_log10_r():
     assert refds is not None, ('Unable to open "%s" dataset.' % reffilename)
     refdata = refds.GetRasterBand(1).ReadAsArray()
 
-    assert numpy.alltrue(data == numpy.log10(refdata))
+    assert numpy.allclose(data, numpy.log10(refdata))
 
 
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