GHA: run badwords check on tests/*.md too

With several wording updates accordingly.

Closes #14412

dist: drop buildconf

The documented and mandated step has been to not use buildconf but to
invoke 'autoreconf -fi' for four years already.

This change only drops buildconf from

dist: drop buildconf

The documented and mandated step has been to not use buildconf but to
invoke 'autoreconf -fi' for four years already.

This change only drops buildconf from the release tarball, it remains
present in git for now.

Follow-up to 85868537d6d5b8

Closes #14412

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tests: provide docs a as curldown, not nroff

As runtests.md and testcurl.md. Very few people actually need these as
manpages anyway.

With this, we have no more nroff formatted d

tests: provide docs a as curldown, not nroff

As runtests.md and testcurl.md. Very few people actually need these as
manpages anyway.

With this, we have no more nroff formatted documents in git.

Closes #14324

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