fix: Change learn-ocaml-www.zip inner dir (www → learn-ocaml-www)

[erikmd]

• Kind: minor bugfix

Description

Motivation: avoid a conflict between "source www" and "generated www",
doing unzip learn-ocaml-www.zip; learn-ocaml build --contents-dir=….

Related: e36d874

Checklist

• Read the CONTRIBUTING.md guide and:
  • Use Atomic Commits so each commit gathers a single logical change
  • Use Conventional Commits regarding commit messages (needed by our release toolchain)

Note to maintainers

• Read this wiki page
• Make sure the PR has a milestone
• Assign yourself before merging
• We can squash-merge 1-commit PRs (use a header with a conventional-commit type, add a footer with Fix #… if need be)