[test] move doctest_skip to pytest command

Tox v4 does not concatenate multiple lines when doing variable
substitution from another section hence the config:

  [params]
  doctest_skip =
   --ignore-glob="*gui.py"
   --ignore-glob="*memento.py"

When used in a commands with `pytest {[params]doctest_skip}` results in
tox 4 generating the commands:

1) pytest '--ignore-glob="*gui.py"'
2) '--ignore-glob="*memento.py"'

The `doctest_skip` variable uses multiple lines since 3b392ab. The
parameter substitution comes from 2014 commit c55ea2f which
introduced `nose_skip` (later renamed `doctest_skip`).

Since the `doctest_skip` parameter is only substitued once, move it to
the pytest doctest command.

With tox 3 (I have added new lines to the lists):

  $ tox -e doctest --showconf
  ...
  [testenv:doctest]
  commands = [
    ['python', '-W', 'error::UserWarning', '-m', 'pwb',
    'generate_user_files', '-family:wikipedia', '-lang:test', '-v'],
    ['pytest', '--version'],
    ['pytest', 'pywikibot', '--doctest-modules',
     '--ignore-glob=*gui.py', '--ignore-glob=*memento.py']
  ]

With tox 4:

  $ tox config -e doctest -k commands
  [testenv:doctest]
  commands =
    python -W error::UserWarning -m pwb generate_user_files -family:wikipedia -lang:test -v
    pytest --version
    pytest pywikibot --doctest-modules '--ignore-glob=*gui.py' '--ignore-glob=*memento.py'

Bug: T345695
Change-Id: Ic92e1ae2996e734431706242ffbc86dd7f6ff633

tox.ini

@@ -9,10 +9,8 @@ envlist =
     hacking-{py36,py39}
 
 [params]
-# gui needs tkinter
-doctest_skip =
-    --ignore-glob="*gui.py"
-    --ignore-glob="*memento.py"
+# Note: tox 4 does not support multiple lines when doing parameters
+# substitution.
 exclude = --exclude make_dist.py,.tox,.git,./*.egg,build,./scripts/i18n/*
 generate_user_files = -W error::UserWarning -m pwb generate_user_files -family:wikipedia -lang:test -v
 
@@ -73,7 +71,10 @@ basepython = python3
 commands =
     python {[params]generate_user_files}
     pytest --version
-    pytest pywikibot --doctest-modules {[params]doctest_skip}
+# gui.py needs tkinter
+# memento.py has too many timeout
+    pytest pywikibot --doctest-modules --ignore-glob="*gui.py" --ignore-glob="*memento.py"
+
 deps =
     pytest >= 7.0.1
     .[eventstreams]