Enable dependabot for GitHub actions, NPM

[tautschnig]

Description of changes:

We shouldn't have to do updates manually.

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• n/a Methods or procedures are documented
• n/a Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

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