ci: update GitHub Actions and add Dependabot

[stefan-jansen]

Summary

• update GitHub Actions references to current upstream releases
• add a shared Dependabot config for github-actions and pip updates
• standardize workflow dependency maintenance across the repo

Updated actions

• actions/checkout -> v6.0.2
• astral-sh/setup-uv -> v8.1.0
• actions/upload-artifact -> v7.0.1
• actions/download-artifact -> v8.0.1
• pypa/gh-action-pypi-publish -> v1.14.0
• cpina/github-action-push-to-another-repository -> v1.7.3
• codecov/codecov-action -> v6.0.0 (where used)

Validation

• actionlint .github/workflows/*.yml
• git diff --check

[Copilot]

Pull request overview

Updates CI/release/docs GitHub Actions references and introduces a centralized Dependabot configuration to standardize automated dependency maintenance (GitHub Actions + Python) across the repository.

Changes:

• Bump versions for several GitHub Actions used in CI, docs deploy, and release workflows.
• Add .github/dependabot.yml with weekly grouped updates for github-actions and pip.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

File	Description
.github/workflows/release.yml	Updates action versions for build artifact upload/download and PyPI publish/release steps.
.github/workflows/docs.yml	Updates checkout/uv setup actions and bumps the deploy-to-website action version.
.github/workflows/ci.yml	Updates checkout/uv setup and artifact upload action versions in CI jobs.
.github/dependabot.yml	Adds weekly Dependabot updates/groups for GitHub Actions and Python (pip).

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