Revert sphinx version to <6.0.0

[ascillitoe]

Revert sphinx to <6.0.0 since the dependabot CI was not actually testing the new 6.x versions. See #700 (comment). sphinx-autodoc-typehints was also bumped so this has been reverted.

Before the bump to 6.x versions we were on <5.1.0. 5.1.x and 5.2.x failed for us due to issues with nbsphinx. However, I've now upgraded to <6.0.0 because 5.3.0 appears to work OK (see below).

[ascillitoe]

Docs compilation errors/warnings with sphinx 5.3.0:

/home/ascillitoe/Software/alibi-detect/alibi_detect/models/pytorch/trainer.py:docstring of alibi_detect.models.pytorch.trainer:1: WARNING: duplicate object description of alibi_detect.models.pytorch.trainer, other instance in api/alibi_detect.models.pytorch, use :noindex: for one of them
/home/ascillitoe/Software/alibi-detect/alibi_detect/models/tensorflow/resnet.py:docstring of alibi_detect.models.tensorflow.resnet:1: WARNING: duplicate object description of alibi_detect.models.tensorflow.resnet, other instance in api/alibi_detect.models.tensorflow, use :noindex: for one of them
/home/ascillitoe/Software/alibi-detect/alibi_detect/models/tensorflow/trainer.py:docstring of alibi_detect.models.tensorflow.trainer:1: WARNING: duplicate object description of alibi_detect.models.tensorflow.trainer, other instance in api/alibi_detect.models.tensorflow, use :noindex: for one of them
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] overview/saving                                                                                                                                                                          
generating indices... genindex py-modindex done
copying notebooks ... [100%] od/methods/vaegmm.ipynb                                                                                                                                                              
highlighting module code... [100%] alibi_detect.utils.warnings                                                                                                                                                    
writing additional pages... search done
copying images... [100%] _static/Alibi_Detect_Logo_rgb.png                                                                                                                                                        
copying static files... done
copying extra files... done
dumping search index in English (code: en)... done
dumping object inventory... done
build succeeded, 4 warnings.

and previously with spinx 5.0.1:

/home/ascillitoe/Software/alibi-detect/alibi_detect/models/pytorch/trainer.py:docstring of alibi_detect.models.pytorch.trainer:1: WARNING: duplicate object description of alibi_detect.models.pytorch.trainer, other instance in api/alibi_detect.models.pytorch, use :noindex: for one of them
/home/ascillitoe/Software/alibi-detect/alibi_detect/models/tensorflow/resnet.py:docstring of alibi_detect.models.tensorflow.resnet:1: WARNING: duplicate object description of alibi_detect.models.tensorflow.resnet, other instance in api/alibi_detect.models.tensorflow, use :noindex: for one of them
/home/ascillitoe/Software/alibi-detect/alibi_detect/models/tensorflow/trainer.py:docstring of alibi_detect.models.tensorflow.trainer:1: WARNING: duplicate object description of alibi_detect.models.tensorflow.trainer, other instance in api/alibi_detect.models.tensorflow, use :noindex: for one of them
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] overview/saving                                                                                                                                                                           
generating indices... genindex py-modindex done
copying notebooks ... [100%] od/methods/vaegmm.ipynb                                                                                                                                                               
highlighting module code... [100%] alibi_detect.utils.warnings                                                                                                                                                     
writing additional pages... search done
copying images... [100%] _static/Alibi_Detect_Logo_rgb.png                                                                                                                                                         
copying static files... done
copying extra files... done
dumping search index in English (code: en)... done
dumping object inventory... done
build succeeded, 4 warnings.

This looks to be the same.