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 shared Dependabot configuration to automate dependency updates across workflows and Python dependencies.

Changes:

• Bump GitHub Actions used in CI, docs, and release workflows to newer pinned versions.
• Add .github/dependabot.yml to manage GitHub Actions and pip dependency update PRs.
• Standardize dependency update grouping/labels/commit message prefixes via Dependabot.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

File	Description
.github/workflows/release.yml	Updates action versions used for building artifacts and publishing/releases.
.github/workflows/docs.yml	Updates action versions used for docs build and deployment.
.github/workflows/ci.yml	Updates action versions used across lint/typecheck/tests/build jobs.
.github/dependabot.yml	Adds weekly grouped Dependabot updates for GitHub Actions and pip dependencies.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.