Python 3.8 environment for ESMValCore

[valeriupredoi]

We'll have to lift the pin to python<3.8 soon so I managed to get us a working environment...minus numba but there's good news for that as well. This is it:

---
name: esmvaltool
channels:
  - conda-forge

dependencies:
  - esmpy
  - iris>=2.2.1
  - fiona
  - graphviz
  - gcc_linux-64
  - libunwind  # Needed for Python3.7+
  # - numba>=0.47.0
  - python>=3.6
  - python-stratify

Note two things: we need fiona from conda (because pip can not find gdal correctly for fiona) and we will have numba=0.47.0 that is built with py38; in fact numba 47 is already available but not yet in the conda json db: https://anaconda.org/numba/numba/files (well, uploaded 9h ago)

[valeriupredoi]

and here's me asking the numba guys about their upcoming py3.8 version https://github.com/numba/numba/issues/4936

[valeriupredoi]

OK so a numba dev kindly told us they will release numba=0.47 on Dec 19 and that'll work with py3.8. Kudos who gonna test then, I'll be gone for Xmas by then :santa:

[mattiarighi]

Still relevant?