ci: update test-gem-installation to work on windows

Also modify test-nokogumbo-compatibility to skip 2.0.4 on Windows
because it's missing the LDFLAGS fix from #2167, #2202, and
nokogumbo#163.

scripts/test-gem-installation

@@ -115,7 +115,7 @@ describe gemspec.full_name do
         it "has ldflags pointing to the shared object file" do
           ldflags = Nokogiri::VERSION_INFO["nokogiri"]["ldflags"]
           if ::RUBY_PLATFORM.match?(/mingw|mswin/)
-            if gemspec.platform.cpu
+            if gemspec.platform.is_a?(Gem::Platform) && gemspec.platform.cpu
               assert_includes(ldflags, "-L#{File.join(nokogiri_lib_dir, ruby_maj_min)}")
             else
               assert_includes(ldflags, "-L#{nokogiri_lib_dir}")

scripts/test-nokogumbo-compatibility

@@ -20,6 +20,16 @@ if Gem::Requirement.new(">= 3.2.0").satisfied_by?(Gem::Version.new(RUBY_VERSION)
   exit 0
 end
 
+nokogumbo_version = if /\d+\.\d+\.\d+/.match?(ARGV[0])
+  ARGV[0]
+end
+
+NOKOGUMBO_WINDOWS_CONSTRAINT = ">= 2.0.5"
+if Gem.win_platform? && !Gem::Requirement.new(NOKOGUMBO_WINDOWS_CONSTRAINT).satisfied_by?(Gem::Version.new(nokogumbo_version))
+  puts "Skip: Nokogumbo must be #{NOKOGUMBO_WINDOWS_CONSTRAINT} on Windows"
+  exit 0
+end
+
 # this line needs to come before the bundler bit, to assert that we're running against an
 # already-installed version (and not some other version that bundler/inline might install if it came
 # first)
@@ -28,10 +38,6 @@ raise "could not find installed gem" unless gemspec
 
 require "bundler/inline"
 
-nokogumbo_version = if /\d+\.\d+\.\d+/.match?(ARGV[0])
-  ARGV[0]
-end
-
 gemfile(true) do
   source "https://rubygems.org"
   gem "minitest"