chore: Lock and sort Python development dependencies

Based on `pip freeze`.

- Avoids breakage in case of incompatible third party upgrades
- Improves consistency between builds

Author: l0b0

requirements-dev.txt

@@ -1,20 +1,16 @@
-mypy==0.812
-flake8==3.8.*
 black==21.4b2
-
 codespell==1.17.1
+coverage==5.2.1
+doc8==0.8.1
+flake8==3.8.4
 ipython==7.16.1
+# https://github.com/pydata/xarray/issues/5299#issuecomment-840730954
+Jinja2==2.11.3
 jsonschema==3.2.0
+mypy==0.812
+nbsphinx==0.7.1
+orjson==3.5.2
 pylint==1.9.1
 Sphinx==3.5.4
 sphinx-autobuild==0.7.1
 sphinxcontrib-fulltoc==1.2.0
-nbsphinx==0.7.1
-coverage==5.2.*
-doc8==0.8.1
-
-# https://github.com/pydata/xarray/issues/5299#issuecomment-840730954
-jinja2<3.0
-
-# optional dependencies
-orjson==3.5.2