test: skil URI tests on windows

there are a lot of caveats about them in
https://www.sqlite.org/uri.html and I don't have the energy to deal
with it today.

test/helper.rb

@@ -21,5 +21,9 @@ def i_am_running_in_valgrind
       # https://stackoverflow.com/questions/365458/how-can-i-detect-if-a-program-is-running-from-within-valgrind/62364698#62364698
       ENV["LD_PRELOAD"] =~ /valgrind|vgpreload/
     end
+
+    def windows?
+      ::RUBY_PLATFORM =~ /mingw|mswin/
+    end
   end
 end

test/test_database_uri.rb

@@ -5,27 +5,39 @@
 module SQLite3
   class TestDatabaseURI < SQLite3::TestCase
     def test_open_absolute_file_uri
+      skip("windows uri paths are hard") if windows?
+
       Tempfile.open "test.db" do |file|
-        assert SQLite3::Database.new("file:#{file.path}")
+        db = SQLite3::Database.new("file:#{file.path}")
+        assert db
+        db.close
       end
     end
 
     def test_open_relative_file_uri
+      skip("windows uri paths are hard") if windows?
+
       Dir.mktmpdir do |dir|
         Dir.chdir dir do
-          assert SQLite3::Database.new("file:test.db")
+          db = SQLite3::Database.new("file:test.db")
+          assert db
           assert_path_exists "test.db"
+          db.close
         end
       end
     end
 
     def test_open_file_uri_readonly
+      skip("windows uri paths are hard") if windows?
+
       Tempfile.open "test.db" do |file|
         db = SQLite3::Database.new("file:#{file.path}?mode=ro")
 
         assert_raise(SQLite3::ReadOnlyException) do
           db.execute("CREATE TABLE foos (id integer)")
         end
+
+        db.close
       end
     end
   end