⬆️ Bump pkg-config from 1.5.1 to 1.5.6

Bumps [pkg-config](https://github.com/ruby-gnome/pkg-config) from 1.5.1 to 1.5.6.
- [Changelog](https://github.com/ruby-gnome/pkg-config/blob/master/NEWS)
- [Commits](ruby-gnome/pkg-config@1.5.1...1.5.6)

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

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -486,7 +486,7 @@ GEM
     pg (1.4.5)
     pghero (3.3.0)
       activerecord (>= 6)
-    pkg-config (1.5.1)
+    pkg-config (1.5.6)
     posix-spawn (0.3.15)
     premailer (1.18.0)
       addressable