Mount .rubocop_todo.yml to enable successful rubocop execution

[Jefffrey]

What are you trying to accomplish?

When following README steps:

dependabot-core/README.md

Lines 409 to 415 in dc7b8d2

	Style is enforced by [RuboCop](https://rubocop.org/). To check for style violations, simply run `rubocop` in
	each of the packages, e.g.
	```bash
	$ cd go_modules
	$ rubocop
	```

Facing issue with running rubocop locally:

dependabot-core$ bin/docker-dev-shell cargo
 > image dependabot/dependabot-core-development-cargo already exists

=> running docker development shell
[dependabot-core-dev] ~ $ cd cargo
[dependabot-core-dev] ~/cargo $ rubocop
Configuration file not found: /home/dependabot/.rubocop_todo.yml
[dependabot-core-dev] ~/cargo $

Fix mount to enable local execution of rubocop

Anything you want to highlight for special attention from reviewers?

How will you know you've accomplished your goal?

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.