Addition of a single b in "rb" to ensure binary stl files are read properly across platform

[Lomholy]

Free-form text area

Please describe what your PR is adding in terms of features or bugfixes:
This PR changes a single Open_File to use "rb" instead of "r" and correspondingly changes the filetype used for the test in Geometry_test.instr.

I hope it is okay that I do not perform mcdoc, c-lint, etc. for this. It works on my mac and the windows, so I hope the checks go through :D

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Development OS / boundary conditions

Please describe what OS you developed and tested your additions on, and if any special dependencies are required:
MacOs Tahoe and windows 11 i think.

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PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution includes patches to an existing component file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)
  • I have ensured that basic use of the component is OK (e.g. an instrument using it compiles?)
  • I have used the mctest utility to test one or more instruments making use of the component (please attach mcviewtest report as screenshot in comments)
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

• My contribution contains something else

  • [ X] Explanation is added in free form text above or below the checklist

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[willend]

@Lomholy I have removed the #define gymnastics to disable binary STL on Windows. Have further added a second test in the instr for binary STL.

[willend]

@Lomholy binary support for STL indeed achieved on Windows - and now tested through CI also. Merging.

[Lomholy]

@willend Nice! Good to see that it worked elsewhere than just locally!