Bump puma from 3.12.4 to 3.12.6 (sass#456)

Bumps [puma](https://github.com/puma/puma) from 3.12.4 to 3.12.6.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](https://github.com/puma/puma/commits)

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

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

Gemfile.lock

@@ -129,7 +129,7 @@ GEM
     padrino-support (0.12.9)
       activesupport (>= 3.1)
     parallel (1.18.0)
-    puma (3.12.4)
+    puma (3.12.6)
     rack (1.6.12)
     rack-conditional (0.3.1)
       rack (>= 1.6.11)