Upgrade nokogiri gem dependency to fix security issue (#1237)

Author: wojtekn

Gemfile.lock

@@ -213,9 +213,9 @@ GEM
     nanaimo (0.3.0)
     naturally (2.2.1)
     nkf (0.2.0)
-    nokogiri (1.18.4-aarch64-linux-gnu)
+    nokogiri (1.18.8-aarch64-linux-gnu)
       racc (~> 1.4)
-    nokogiri (1.18.4-arm64-darwin)
+    nokogiri (1.18.8-arm64-darwin)
       racc (~> 1.4)
     octokit (6.1.1)
       faraday (>= 1, < 3)