Fix some errors detected by make check

This fixes some trailing whitespaces and errors detected by codespell.

(swh) ✔ ~/swh/swh-environment/swh-docs [master|●1⚑ 4] 
17:16 $ make check
pre-commit run --all-files
Trim Trailing Whitespace.................................................Failed
- hook id: trailing-whitespace
- exit code: 1
- files were modified by this hook

Fixing docs/contributing/tutorial-docs-contribution.rst
Fixing sysadm/user-management/onboarding.rst
Fixing sysadm/user-management/keycloak/authentification.rst
Fixing sysadm/user-management/outboarding.rst
Fixing sysadm/user-management/keycloak/how-to-user-perms.rst
Fixing sysadm/user-management/how-to-manage-creds-store.rst

Check JSON...........................................(no files to check)Skipped
Check Yaml...............................................................Passed
flake8...................................................................Passed
codespell................................................................Failed
- hook id: codespell
- exit code: 2

docs/journal.rst:306: Ot  ==> To, of, or
sysadm/user-management/keycloak/authentification.rst:3: Authentification  ==> Authentication
sysadm/user-management/keycloak/index.rst:8: authentification  ==> authentication

mypy.....................................................................Passed
isort....................................................................Passed
black....................................................................Passed
make: *** [../Makefile.python:28: check] Error 1

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Migrated from D6490 (view on Phabricator)