CI: Enabled OpenCL tests on Linux and OpenGL tests on Windows

[t20100]

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• The PR title is formatted as: <Module or Topic>: <Action> <Summary> (see contributing guidelines)

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This PR enables:

• OpenCL tests on Linux in github actions by using Intel OpenCL ICD (adapted from pyFAI config, thanks @kif !).
• OpenGL tests on Windows in github actions by a software rasterisation mesa OpenGL lib as it was done on appveyor.

It also explicitly enables/disables OpenCL tests depending on the platforms:

• Disabled on ubuntu-20.04 because it seg fault. I used suspect the ICD to be incompatible with ubuntu 20.04.
• Disabled on Windows because installation of OpenCL is not done (yet).

OpenGL tests are now enabled on all platforms

[t20100]

Ready for review

[t20100]

Also enable OpenGL tests on Windows