Bump puma from 3.12.2 to 3.12.6 in /books_db_api

Bumps [puma](https://github.com/puma/puma) from 3.12.2 to 3.12.6.
- [Release notes](https://github.com/puma/puma/releases)
- [Changelog](https://github.com/puma/puma/blob/master/History.md)
- [Commits](puma/puma@v3.12.2...v3.12.6)

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

books_db_api/Gemfile.lock

@@ -80,7 +80,7 @@ GEM
       method_source (~> 0.9.0)
     pry-rails (0.3.9)
       pry (>= 0.10.4)
-    puma (3.12.2)
+    puma (3.12.6)
     racc (1.5.2)
     rack (2.2.3)
     rack-test (1.1.0)