Update dask requirement, disabled example

[eddiebergman]

Updates dask to 2021.12.0. Disables example as a result.

The docs won't build properly due to sphinx issues encountered that are solved in development with PR #1339.

Additionally, an issue with manual spawning occures so the example example_parallel_manual_spawning_python.py was disabled. See the issue dask/distributed#5627

[codecov]

Codecov Report

Merging #1356 (f0f04b0) into master (7364c68) will decrease coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1356      +/-   ##
==========================================
- Coverage   88.13%   88.05%   -0.09%     
==========================================
  Files         140      140              
  Lines       11163    11163              
==========================================
- Hits         9839     9830       -9     
- Misses       1324     1333       +9     

Impacted Files	Coverage Δ
autosklearn/__version__.py	100.00% <100.00%> (ø)
...mponents/feature_preprocessing/nystroem_sampler.py	85.29% <0.00%> (-5.89%)	⬇️
autosklearn/util/dependencies.py	93.22% <0.00%> (-1.70%)	⬇️
autosklearn/util/logging_.py	88.96% <0.00%> (-1.38%)	⬇️
...learn/pipeline/components/regression/libsvm_svr.py	90.24% <0.00%> (-1.22%)	⬇️
...ine/components/classification/gradient_boosting.py	93.04% <0.00%> (-0.87%)	⬇️

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