gh-36373: Enable conda ci for all PRs and remove experimental label
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Using conda to install all sage dependencies is pretty stable and has
been long enough in "experimental mode". We remove here the experimental
flag and in order to make sure that the workflow is not breaking enable
the conda-ci on all PRs. This also provides a) faster feedback as the
whole build+test takes only about 1.5h (which is less time then what
only the "incremental build" currently takes) and b) tests that the code
is working on all supported python versions. The last remaining failing
tests under linux are temporarily disabled in
https://github.com/sagemath/sage/pull/36372.
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URL: https://github.com/sagemath/sage/pull/36373
Reported by: Tobias Diez
Reviewer(s): Matthias Köppe
