Add tests covering "+00:00" and 0 with Time#localtime and Time.at.

See ruby/spec#1285

Author: philr

spec/ruby/core/time/utc_spec.rb

@@ -43,10 +43,14 @@
 
   it "does not treat time with +00:00 offset as UTC" do
     Time.new(2022, 1, 1, 0, 0, 0, "+00:00").utc?.should == false
+    Time.now.localtime("+00:00").utc?.should == false
+    Time.at(Time.now, in: "+00:00").utc?.should == false
   end
 
   it "does not treat time with 0 offset as UTC" do
     Time.new(2022, 1, 1, 0, 0, 0, 0).utc?.should == false
+    Time.now.localtime(0).utc?.should == false
+    Time.at(Time.now, in: 0).utc?.should == false
   end
 end