Use new GitHub action for creating releases

[dlachaume]

Content

This PR includes updates of the CI jobs that create pre-release and release to replace the unmaintained marvinpinto/action-automatic-releases action.

The https://github.com/softprops/action-gh-release is a suitable replacement for the pre-release job as it can handle the tasks previously managed by both marvinpinto/action-automatic-releases and tubone24/update_release , including updating the release notes body.

Examples of releases created from a fork of Mithril using these new GitHub Action: https://github.com/dlachaume/mithril/releases

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • CHANGELOG file is updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • No clippy warnings in the CI
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested
• Documentation
  • Update README file (if relevant)
  • Update documentation website (if relevant)
  • Add dev blog post (if relevant)

Issue(s)

Relates to #1691

[github-actions]

Test Results

    4 files  ±0     54 suites  ±0   9m 31s ⏱️ +6s
1 351 tests ±0  1 351 ✅ ±0  0 💤 ±0  0 ❌ ±0 
1 559 runs  ±0  1 559 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit e8e634c. ± Comparison against base commit 0bc09f4.

♻️ This comment has been updated with latest results.

[jpraynaud]

LGTM 👍