RTD: remove transitive deps from docs env

[mathause]

This adds all of our direct dependencies to the docs environment (following #448) but removes the transitive ones. The direct ones were installed before, just not explicitly listed. Unfortunately sphinx (or maybe just the autosummary extension) imports the functions it wants to create the docs for, so they must be installed. However, leaving the optional transitive deps away should lead to a small speed up.

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Alternatively we could install everything using pip but that would be more work (c.f. regionmask/regionmask#450)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.73%. Comparing base (9b0b76b) to head (2969028).
Report is 43 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #449      +/-   ##
==========================================
- Coverage   87.90%   83.73%   -4.18%     
==========================================
  Files          40       44       +4     
  Lines        1745     1949     +204     
==========================================
+ Hits         1534     1632      +98     
- Misses        211      317     +106     

Flag	Coverage Δ
unittests	83.73% <ø> (-4.18%)	⬇️

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[veni-vidi-vici-dormivi]

Ah another one.

Alternatively we could install everything using pip but that would be more work

Would that remove the need for the docs to have its own yml?

[mathause]

Potentially - we could use the docs extra for the installation, so python -m pip install .[docs]. That's another good reason for switching.

(As long as we don't need any non-python dependency [which was the ultimate problem in regionmask/regionmask#450])

[mathause]

I suggest to merge this and try the pip installation in another PR (see #453)

[veni-vidi-vici-dormivi]

Why do we remove the version?

[mathause]

Something less to keep track of. It should per default install the newest versions. (But yes there are also arguments for keeping it - so no real good reason).