CI: Tell dependabot to update GH Actions

[olleolleolle]

This PR adds a configuration to tell Dependabot to update the versions used for some well-known GitHub Actions, such as checkout, in order to avoid deprecation warnings when those get too old. Documentation

Update:

Here are some warnings that some of the Actions output currently:

Analyze (ruby)

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3, github/codeql-action/init@v2, github/codeql-action/autobuild@v2, github/codeql-action/analyze@v2. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

Analyze (ruby)

CodeQL Action v2 will be deprecated on December 5th, 2024. Please update all occurrences of the CodeQL Action in your workflow files to v3. For more information, see https://github.blog/changelog/2024-01-12-code-scanning-deprecation-of-codeql-action-v2/