* fix(lock-closed): update `policyUrl` in `bundle.js`

In #77, `policyUrl` was fixed in `src/main.ts`, but not in the built
file that is actually used when running the action (`lib/bundle.js`).
As a result, the change did not take effect.

This commit updates `policyUrl` to `lib/bundle.js` as well. This will
help address angular/angular#39358 (once [lock-closed.yml][1] is updated
in all affected repositories).

[1]: https://github.com/angular/angular/blob/cfac8e0764498713f63a2335b46823e8a9b285c5/.github/workflows/lock-closed.yml#L13

* fix(lock-closed): fix `main` field in `package.json`

Change the `main` field in `package.json` to point to the correct file,
i.e. `lib/bundle.js` instead of `lib/main.js`.

This doesn't have any practical effect, since [action.yml][1] specifies
the actual entry-point used for the action, but it avoids confusion.

[1]: https://github.com/angular/dev-infra/blob/414834b2b24dd2df37c6ed00808387ee6fd91b66/github-actions/lock-closed/action.yml#L13

* docs(lock-closed): update `inputs` in `action.yml` (github-token --> lock-bot-token)

In PR #40, the authentication used by the `lock-closed` action was
changed. As part of this change, the `github-token` input parameter was
replaced by `lock-bot-token`. However, `lock-closed/action.yml` was not
updated accordingly, resulting in the following warning ([example][1]):

> Unexpected input(s) 'lock-bot-key', valid inputs are
> ['github-token', 'locks-per-execution']

This commit gets rid of the warnings by updating `action.yml` to list
the correct inputs.

[1]: https://github.com/angular/angular/actions/runs/318094899