Avoid redundant `time.getutc` call if it is already utc time object

Currently `type.serialize` and `connection.{quote|type_cast}` for a time
object always does `time.getutc` call regardless of whether it is
already utc time object or not, that duplicated proccess
(`connection.type_cast(type.serialize(time))`) allocates extra/useless
time objects for each type casting.

This avoids that redundant `time.getutc` call if it is already utc time
object. In the case of a model has timestamps (`created_at` and
`updated_at`), it avoids 6,000 time objects allocation for 1,000 times
`model.save`.

```ruby
ObjectSpace::AllocationTracer.setup(%i{path line type})

pp ObjectSpace::AllocationTracer.trace {
  1_000.times { User.create }
}.select { |k, _| k[0].end_with?("quoting.rb", "time_value.rb") }
```

Before (c104bfe424e6cebe9c8e85a38515327a6c88b1f8):

```
{["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  203,
  :T_ARRAY]=>[1004, 0, 778, 0, 1, 0],
 ["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  220,
  :T_STRING]=>[2, 0, 2, 1, 1, 0],
 ["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  209,
  :T_ARRAY]=>[8, 0, 8, 1, 1, 0],
 ["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  57,
  :T_ARRAY]=>[4, 0, 4, 1, 1, 0],
 ["~/rails/activemodel/lib/active_model/type/helpers/time_value.rb",
  17,
  :T_DATA]=>[4000, 0, 3096, 0, 1, 0],
 ["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  120,
  :T_DATA]=>[2000, 0, 1548, 0, 1, 0],
 ["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  126,
  :T_STRING]=>[4000, 0, 3096, 0, 1, 0]}
```

After (this change):

```
{["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  203,
  :T_ARRAY]=>[1004, 0, 823, 0, 1, 0],
 ["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  220,
  :T_STRING]=>[2, 0, 2, 1, 1, 0],
 ["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  209,
  :T_ARRAY]=>[8, 0, 8, 1, 1, 0],
 ["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  57,
  :T_ARRAY]=>[4, 0, 4, 1, 1, 0],
 ["~/rails/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb",
  126,
  :T_STRING]=>[2000, 0, 1638, 0, 1, 0]}
```

2 files changed, 5 insertions, 5 deletions

diff --git a/activemodel/lib/active_model/type/helpers/time_value.rb b/activemodel/lib/active_model/type/helpers/time_value.rb
index 508fe77531..075e906034 100644
--- a/activemodel/lib/active_model/type/helpers/time_value.rb
+++ b/activemodel/lib/active_model/type/helpers/time_value.rb
@@ -11,10 +11,10 @@ module ActiveModel
           value = apply_seconds_precision(value)
 
           if value.acts_like?(:time)
-            zone_conversion_method = is_utc? ? :getutc : :getlocal
-
-            if value.respond_to?(zone_conversion_method)
-              value = value.send(zone_conversion_method)
+            if is_utc?
+              value = value.getutc if value.respond_to?(:getutc) && !value.utc?
+            else
+              value = value.getlocal if value.respond_to?(:getlocal)
             end
           end
 
diff --git a/activemodel/lib/active_model/type/value.rb b/activemodel/lib/active_model/type/value.rb
index 994d135b7b..788ded3e96 100644
--- a/activemodel/lib/active_model/type/value.rb
+++ b/activemodel/lib/active_model/type/value.rb
@@ -110,7 +110,7 @@ module ActiveModel
         [self.class, precision, scale, limit].hash
       end
 
-      def assert_valid_value(*)
+      def assert_valid_value(_)
       end
 
       private