Use Miniforge installer in GutHub actions

[antonwolfy]

Based on information stated here:

With the Miniforge 23.3.1 release, the Miniforge and Mambaforge installers became essentially identical. The only difference between the two was their name and, subsequently, the default installation directory.

The PR proposes to remove miniforge-variant: Mambaforge option from the setup of conda-incubator/setup-miniconda per each affected GitHub action. The removed option will assume to use Miniforge installer inside the actions and will help to get rid of deprecation warning in the logs.

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[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/index.html

[vtavana]

Thank you, @antonwolfy!