Revert "CI: bundle down nokogiri to 1.13"

This reverts commit c5e9f12.

Author: amatsuda

test_projects/rails/rspec_rails/Gemfile

@@ -13,8 +13,6 @@ else
   gem "sqlite3", "~> 1.4"
 end
 
-gem "nokogiri", "~> 1.13.10"
-
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem "rails", "~> 6.1.4"
 # Use Puma as the app server

test_projects/rails/rspec_rails/Gemfile.lock

@@ -112,10 +112,10 @@ GEM
     msgpack (1.3.3-java)
     nio4r (2.5.4)
     nio4r (2.5.4-java)
-    nokogiri (1.13.10)
-      mini_portile2 (~> 2.8.0)
+    nokogiri (1.15.2)
+      mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
-    nokogiri (1.13.10-java)
+    nokogiri (1.15.2-java)
       racc (~> 1.4)
     public_suffix (4.0.7)
     puma (5.1.1)
@@ -212,7 +212,6 @@ DEPENDENCIES
   byebug
   capybara (>= 3.36.0)
   jbuilder (~> 2.7)
-  nokogiri (~> 1.13.10)
   puma (~> 5.0)
   rails (~> 6.1.4)
   rspec-rails