Bug#951768: skimage documentation build fails with python 3.8

[Matthias Klose]

Package: src:skimage
Version: 0.16.2-2
Severity: important
Tags: sid bullseye
User: debian-python at lists.debian.org
Usertags: python3.8

the skimage documentation build fails with python 3.8:

[...]
copying static files... done
copying extra files... done
dumping search index in English (code: en) ... done
dumping object inventory... done
build succeeded, 146 warnings.

The HTML pages are in build/html.

Exception occurred:
  File "/usr/lib/python3/dist-packages/sphinx_gallery/gen_gallery.py", line 311,
in sumarize_failing_examples
    raise ValueError("Here is a summary of the problems encountered when "
ValueError: Here is a summary of the problems encountered when running the examples

Unexpected failing examples:
/<<PKGBUILDDIR>>/doc/examples/segmentation/plot_boundary_merge.py failed leaving
traceback:
Traceback (most recent call last):
  File "/<<PKGBUILDDIR>>/doc/examples/segmentation/plot_boundary_merge.py", line 1
    ============================================
    ^
SyntaxError: invalid syntax


/<<PKGBUILDDIR>>/doc/examples/data/plot_scientific.py failed leaving traceback:
Traceback (most recent call last):
  File "/<<PKGBUILDDIR>>/doc/examples/data/plot_scientific.py", line 1
    =================
    ^
SyntaxError: invalid syntax


/<<PKGBUILDDIR>>/doc/examples/segmentation/plot_marked_watershed.py failed
leaving traceback:
Traceback (most recent call last):
  File "/<<PKGBUILDDIR>>/doc/examples/segmentation/plot_marked_watershed.py", line 1
    ===============================
    ^
SyntaxError: invalid syntax