Bump VERSION to 1.8.0

• Diff: https://gitlab.com/gitlab-org/gitlab-triage/compare/v1.7.1...8782f99828c16b1eb12cbccc5629f8202508006a

• Release notes:

### New scenarios and scenario updates

- !150 Add `comment_type: thread` action.
- !152 Add `--all-projects` option.
- !153 Add `move` action.

### Fixes

- !144 Make sure we don't render HTML at all.
- !145 Fix the example policy file, show real world examples.

### Doc changes

- !151 Fixed old style no label reference to new format.

### Other changes (CI, backstage)

- !142 Add release automation and refactor CI config.
- !146 Set 'workflow:rules', 'default', and 'rules'.
- !149 Run 'gem install' without any flag.
- !154 Bump VERSION to 1.8.0
- !155 Fix fetching the version, avoiding using bundler
- !156 Fix and release 1.8.0

• Checklist before merging:

  • Diff link is up-to-date.
  • Based on the diff, lib/gitlab/triage/version.rb is updated, according to SemVer.
  • Release notes are accurate.

• Checklist after merging:

  • Update the release notes for the newly created tag.