ref: include py.typed in installed package

[asottile-sentry]

119 added the marker but it is ~useless without it being in the installed package

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[conventional-commit-lint-gcf[bot]]

🤖 I detect that the PR title and the commit message differ and there's only one commit. To use the PR title for the commit history, you can use Github's automerge feature with squashing, or use automerge label. Good luck human!

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