Bump danger/swift from 3.15.0 to 3.21.2

Bumps [danger/swift](https://github.com/danger/swift) from 3.15.0 to 3.21.2.
- [Release notes](https://github.com/danger/swift/releases)
- [Changelog](https://github.com/danger/swift/blob/master/CHANGELOG.md)
- [Commits](https://github.com/danger/swift/compare/3.15.0...3.21.2)

---
updated-dependencies:
- dependency-name: danger/swift
  dependency-version: 3.21.2
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/danger.yml

@@ -16,7 +16,7 @@ jobs:
         with:
           fetch-depth: 0
       - name: danger/swift
-        uses: danger/swift@3.15.0
+        uses: danger/swift@3.21.2
         with:
           args: --failOnErrors --no-publish-check
         env: