Restore ActiveRecord.default_timezone after #234 regression test

The new test set ActiveRecord.default_timezone = :utc but did not put
the original value back, so it could affect tests that ran later in
the same process. Capture the original value and restore it from the
ensure block alongside the deprecator behavior.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yahonda

spec/plsql/schema_spec.rb

@@ -221,6 +221,7 @@ class TestModel < TestBaseModel
   it "should not emit ActiveRecord::Base.default_timezone deprecation warning (#234)" do
     skip "ActiveRecord.default_timezone is not available" unless ActiveRecord.respond_to?(:default_timezone=)
 
+    original_default_timezone = ActiveRecord.default_timezone
     ActiveRecord.default_timezone = :utc
 
     deprecator = ActiveRecord.respond_to?(:deprecator) ? ActiveRecord.deprecator : ActiveSupport::Deprecation
@@ -231,6 +232,7 @@ class TestModel < TestBaseModel
       expect(plsql.default_timezone).to eq(:utc)
     ensure
       deprecator.behavior = original_behavior
+      ActiveRecord.default_timezone = original_default_timezone
     end
 
     expect(warnings.grep(/default_timezone/)).to be_empty