ci: update Dependabot to also update Rust dependencies

[georglauterbach]

Description

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under documentation/)
• If necessary, I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes