Bump tinymce from 6.7.1 to 6.7.3

Bumps [tinymce](https://github.com/tinymce/tinymce/tree/HEAD/modules/tinymce) from 6.7.1 to 6.7.3.
- [Changelog](https://github.com/tinymce/tinymce/blob/develop/modules/tinymce/CHANGELOG.md)
- [Commits](https://github.com/tinymce/tinymce/commits/6.7.3/modules/tinymce)

---
updated-dependencies:
- dependency-name: tinymce
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>