PULL_REQUEST_TEMPLATE.md

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- [ ] At least two implementers are interested (and none opposed):
   * …
   * …
- [ ] [Tests](https://github.com/web-platform-tests/wpt) are written and can be reviewed and commented upon at:
   * … <!-- If these tests are tentative, link a PR to make them non-tentative. -->
- [ ] [Implementation bugs](https://github.com/whatwg/meta/blob/main/MAINTAINERS.md#handling-pull-requests) are filed:
   * Chromium: …
   * Gecko: …
   * WebKit: …
   * Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): …
   * Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): …
- [ ] [MDN issue](https://github.com/whatwg/meta/blob/main/MAINTAINERS.md#handling-pull-requests) is filed: …
- [ ] The top of this comment includes a [clear commit message](https://github.com/whatwg/meta/blob/main/COMMITTING.md) to use. <!-- If you created this PR from a single commit, Github copied its message. Otherwise, you need to add a commit message yourself. -->

(See [WHATWG Working Mode: Changes](https://whatwg.org/working-mode#changes) for more details.)