tests: avoid non-portable sed command
sed -i is a GNU extension and the i command without newline as well.
Just create the file from scratch with printf to side-step the issue.
include CHANGELOG
include COPYING
include hgext3rd/topic/README
include MANIFEST.in
include README
include setup.py
recursive-include tests *.py *.sh *.t
include docs/makefile
include docs/*.py
include docs/README
include docs/*.rst
include docs/static/*.svg
include docs/tutorials/*.t
include docs/tutorial/standalone.html
recursive-include docs/figures *.svg *.png
recursive-include docs/tutorial *.css *.js *.md *.py *.rst *.sh *.t
exclude docs/tutorial/.netlify
exclude .gitlab-ci.yml
exclude ./hgext3rd/evolve/legacy.py
exclude .hg-format-source
exclude Makefile
exclude tests/test-drop.t
exclude tests/test-inhibit.t
exclude tests/test-oldconvert.t
prune contrib
prune debian
prune .gitlab
prune hgext3rd/evolve/hack