I signed into the tedium-bot (Polymer automation account) GitHub page, created a Personal access token, and added it to this repo's secrets as TEDIUM_BOT_GITHUB_ACCESS_TOKEN.
By using this token instead of the automatically populated GITHUB_TOKEN token, subsequent GitHub Actions will be allowed to run on the PR we create (i.e. tests).
This adds a GitHub action called bump-mdc-deps that automatically runs
the script that pins our MDC Web deps to the latest canary version, and
sends us a PR if it has changed.