Apply swh-py-template v0.3.3 with copier

Jenkins job DLDBASE/gitlab-builds #391 succeeded in 2 min 26 sec.
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added 3 commits

• e5bf1897 - Apply swh-py-template v0.3.3 with copier
• a75a5039 - tests: Fix flake8 warning
• 1ea3e051 - docs/package-loader-specifications: Fix typo detected by codespell

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Jenkins job DLDBASE/gitlab-builds #392 succeeded in 6 min 2 sec.
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merged manually