Bump nokogiri from 1.14.3 to 1.15.6 in /sinatra

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.14.3 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@v1.14.3...v1.15.6)

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

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

sinatra/Gemfile.lock

@@ -1,15 +1,15 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    mini_portile2 (2.8.4)
+    mini_portile2 (2.8.5)
     minitest (5.14.4)
     mustermann (2.0.2)
       ruby2_keywords (~> 0.0.1)
-    nokogiri (1.14.3)
-      mini_portile2 (~> 2.8.0)
+    nokogiri (1.15.6)
+      mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
     nori (2.6.0)
-    racc (1.7.1)
+    racc (1.7.3)
     rack (2.2.8.1)
     rack-parser (0.7.0)
       rack