Check if `Kernel#untaint` is defined instead of version comparison

Probably `RUBY_VERSION` seems overwritten somewhere in the tests.

lib/bundler/dsl.rb

@@ -46,7 +46,7 @@ module Bundler
       @gemfile = expanded_gemfile_path
       @gemfiles << expanded_gemfile_path
       contents ||= Bundler.read_file(@gemfile.to_s)
-      instance_eval(contents.dup.tap{|x| x.untaint if RUBY_VERSION < "2.7" }, gemfile.to_s, 1)
+      instance_eval(contents.dup.tap{|x| x.untaint if Kernel.method_defined?(:untaint) }, gemfile.to_s, 1)
     rescue Exception => e # rubocop:disable Lint/RescueException
       message = "There was an error " \
         "#{e.is_a?(GemfileEvalError) ? "evaluating" : "parsing"} " \

lib/bundler/rubygems_ext.rb

@@ -29,7 +29,7 @@ module Gem
       # gems at that time, this method could be called inside another require,
       # thus raising with that constant being undefined. Better to check a method
       if source.respond_to?(:path) || (source.respond_to?(:bundler_plugin_api_source?) && source.bundler_plugin_api_source?)
-        Pathname.new(loaded_from).dirname.expand_path(source.root).to_s.tap{|x| x.untaint if RUBY_VERSION < "2.7" }
+        Pathname.new(loaded_from).dirname.expand_path(source.root).to_s.tap{|x| x.untaint if Kernel.method_defined?(:untaint) }
       else
         rg_full_gem_path
       end

lib/bundler/shared_helpers.rb

@@ -13,13 +13,13 @@ module Bundler
     def root
       gemfile = find_gemfile
       raise GemfileNotFound, "Could not locate Gemfile" unless gemfile
-      Pathname.new(gemfile).tap{|x| x.untaint if RUBY_VERSION < "2.7" }.expand_path.parent
+      Pathname.new(gemfile).tap{|x| x.untaint if Kernel.method_defined?(:untaint) }.expand_path.parent
     end
 
     def default_gemfile
       gemfile = find_gemfile
       raise GemfileNotFound, "Could not locate Gemfile" unless gemfile
-      Pathname.new(gemfile).tap{|x| x.untaint if RUBY_VERSION < "2.7" }.expand_path
+      Pathname.new(gemfile).tap{|x| x.untaint if Kernel.method_defined?(:untaint) }.expand_path
     end
 
     def default_lockfile
@@ -28,7 +28,7 @@ module Bundler
       case gemfile.basename.to_s
       when "gems.rb" then Pathname.new(gemfile.sub(/.rb$/, ".locked"))
       else Pathname.new("#{gemfile}.lock")
-      end.tap{|x| x.untaint if RUBY_VERSION < "2.7" }
+      end.tap{|x| x.untaint if Kernel.method_defined?(:untaint) }
     end
 
     def default_bundle_dir
@@ -100,7 +100,7 @@ module Bundler
     #
     # @see {Bundler::PermissionError}
     def filesystem_access(path, action = :write, &block)
-      yield(path.dup.tap{|x| x.untaint if RUBY_VERSION < "2.7" })
+      yield(path.dup.tap{|x| x.untaint if Kernel.method_defined?(:untaint) })
     rescue Errno::EACCES
       raise PermissionError.new(path, action)
     rescue Errno::EAGAIN
@@ -236,7 +236,7 @@ module Bundler
 
     def search_up(*names)
       previous = nil
-      current  = File.expand_path(SharedHelpers.pwd).tap{|x| x.untaint if RUBY_VERSION < "2.7" }
+      current  = File.expand_path(SharedHelpers.pwd).tap{|x| x.untaint if Kernel.method_defined?(:untaint) }
 
       until !File.directory?(current) || current == previous
         if ENV["BUNDLER_SPEC_RUN"]

lib/bundler/source/git.rb

@@ -336,7 +336,7 @@ module Bundler
 
       def load_gemspec(file)
         stub = Gem::StubSpecification.gemspec_stub(file, install_path.parent, install_path.parent)
-        stub.full_gem_path = Pathname.new(file).dirname.expand_path(root).to_s.tap{|x| x.untaint if RUBY_VERSION < "2.7" }
+        stub.full_gem_path = Pathname.new(file).dirname.expand_path(root).to_s.tap{|x| x.untaint if Kernel.method_defined?(:untaint) }
         StubSpecification.from_stub(stub)
       end