Bump strong_migrations from 1.6.3 to 1.6.4 (#545)

Bumps [strong_migrations](https://github.com/ankane/strong_migrations) from 1.6.3 to 1.6.4.
- [Changelog](https://github.com/ankane/strong_migrations/blob/master/CHANGELOG.md)
- [Commits](ankane/strong_migrations@v1.6.3...v1.6.4)

---
updated-dependencies:
- dependency-name: strong_migrations
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -327,7 +327,7 @@ GEM
       rubocop-performance (~> 1.19.0)
     stimulus-rails (1.3.0)
       railties (>= 6.0.0)
-    strong_migrations (1.6.3)
+    strong_migrations (1.6.4)
       activerecord (>= 5.2)
     thor (1.3.0)
     timeout (0.4.0)