[MRG] fix docs building for pip 22.2

[ctb]

This PR fixes #2139.

In brief, docs building failed on readthedocs immediately after pip 22.2 was released. It looks very similar to pypa/pip#11294 which is caused by some underlying distutils interaction.

The fix is to ask the conda environment for docs building to use python=3.10, in doc/environment.yml.

This PR also adds pip to the doc/environment.yml file per this message in the readthedocs build -

Warning: you have pip-installed dependencies in your environment file, but you do not list pip itself as one of your conda dependencies.  Conda may not use the correct pip to install your packages, and they may end up in the wrong place.  Please add an explicit pip dependency.  I'm adding one for you, but still nagging you.

[codecov]

Codecov Report

Merging #2143 (5bd6560) into latest (61f37a7) will increase coverage by 7.38%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           latest    #2143      +/-   ##
==========================================
+ Coverage   84.31%   91.70%   +7.38%     
==========================================
  Files         130       99      -31     
  Lines       15293    11017    -4276     
  Branches     2167     2167              
==========================================
- Hits        12895    10103    -2792     
+ Misses       2095      611    -1484     
  Partials      303      303              

Flag	Coverage Δ
python	91.70% <ø> (ø)
rust	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/core/src/ffi/index/mod.rs
src/core/src/sketch/hyperloglog/mod.rs
src/core/tests/test.rs
src/core/src/storage.rs
src/core/src/index/revindex.rs
src/core/src/errors.rs
src/core/src/index/sbt/mhbt.rs
src/core/src/ffi/mod.rs
src/core/src/sketch/hyperloglog/estimators.rs
src/core/src/cmd.rs
... and 21 more

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[ctb]

Build succeeded - see https://readthedocs.org/projects/sourmash/builds/17522357/! 🎉

@sourmash-bio/devs ready for review and merge.

[bluegenes]

Lgtm!

[ctb]

thanks!