build(deps-dev): bump nokogiri from 1.15.2 to 1.15.6 in /bindings/ruby

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.15.2 to 1.15.6.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.15.2...v1.15.6)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-type: direct:development
...

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

Author: dependabot[bot]

Diff for: bindings/ruby/Gemfile.lock

@@ -13,16 +13,16 @@ GEM
       addressable
     diff-lcs (1.5.0)
     htmlentities (4.3.4)
-    mini_portile2 (2.8.2)
-    nokogiri (1.15.2)
+    mini_portile2 (2.8.5)
+    nokogiri (1.15.6)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
     premailer (1.21.0)
       addressable
       css_parser (>= 1.12.0)
       htmlentities (>= 4.0.0)
     public_suffix (5.0.1)
-    racc (1.7.1)
+    racc (1.7.3)
     rake (13.0.6)
     rake-compiler (1.2.3)
       rake