ImathTest fails on mingw32

[cary-ilm]

ImathTest fails with what appear to be numerical precision issues:

Assertion failed: f1.worldRadius (v3, one) == f1.worldRadiusExc (v3, one), file D:/a/Imath/Imath/src/ImathTest/testFrustum.cpp, line 449
Assertion failed: b21 == b2, file D:/a/Imath/Imath/src/ImathTest/testBoxAlgo.cpp, line 830

To activate the failure in the CI checks, remove this line in .githhub/work/ci_workflow.yml:

BUILD_TESTING: 'OFF' # TODO: Imath.testMatrix fails, please help find why!