Update Imath to version 3.1.5 / rev 3 via SR 984410
    
    https://build.opensuse.org/request/show/984410
    by user pgajdos + dimstar_suse
    - update to 3.1.5:
      * Update CI workflow matrix for VFX-CY2022
      * Use _WIN32 instead of _MSC_VER to fix mingw build
      * Fix 32-bit x86 build failure with 16c instructions
      * Move numeric_limits specializations into half.h
      * Change references to "master" branch to "main"
      * Remove some simple typos in the code
      * Added missing check _M_IX86 or _M_X64 when using __lzcnt.
      * SolveNormalizedCubic fix to return proper real root
      * Add docs target only if not a subproject
      * Fix docs race condition and make installation optional
      * Remove dead PyImath code and references to ilmbase
      * Use equalWithAbsError instead of equal operator for float
      * Fix sphinx warnings and man page filenames
      * Adding missing stdexcept header
      * for better SIMD auto-vectorization
      * Remove extra projec