Automatically merge Dependabot pull requests

[dolfinus]

Hello.

I see that Dependabot integration is set up on your repo. Here I propose to add an automatic step of merging pull requests from this bot if tests have been passed successfully.

The only thing should be done for enabling this feature is generating new personal token with write repo write access and saving it as PERSONAL_TOKEN secret.

This is because events made using Github Actions token, like rebasing the branch and pushing commits, do not trigger workflow runs.
This leads to strange issues - for example, you've set branch protection rule and checked some workflow as mandatory (e.g. running tests), and then 2 Dependabot merge requests were created. First MR was approved and merged automatically, then the second MR was rebased by this action, but now workflow haven't been started this MR cannot be merged automatically.
Using personal access token instead of GITHUB_TOKEN solves this issue.

[dolfinus]

@Betree Could you please take a look?