Correctly handle infinity value in PostgreSQL range type

An empty string is an invalid value in Ruby's range class.
So need to handle `Float::INFINITY` as it is and cast it in
`encode_range`.

Fixes #31612

activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb

@@ -60,7 +60,7 @@ module ActiveRecord
             end
 
             def type_cast_single_for_database(value)
-              infinity?(value) ? "" : @subtype.serialize(value)
+              infinity?(value) ? value : @subtype.serialize(value)
             end
 
             def extract_bounds(value)

activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb

@@ -138,7 +138,7 @@ module ActiveRecord
           end
 
           def encode_range(range)
-            "[#{type_cast(range.first)},#{type_cast(range.last)}#{range.exclude_end? ? ')' : ']'}"
+            "[#{type_cast_range_value(range.first)},#{type_cast_range_value(range.last)}#{range.exclude_end? ? ')' : ']'}"
           end
 
           def determine_encoding_of_strings_in_array(value)
@@ -154,6 +154,14 @@ module ActiveRecord
             else _type_cast(values)
             end
           end
+
+          def type_cast_range_value(value)
+            infinity?(value) ? "" : type_cast(value)
+          end
+
+          def infinity?(value)
+            value.respond_to?(:infinite?) && value.infinite?
+          end
       end
     end
   end

activerecord/test/cases/adapters/postgresql/range_test.rb

@@ -358,6 +358,18 @@ _SQL
       end
     end
 
+    def test_infinity_values
+      PostgresqlRange.create!(int4_range: 1..Float::INFINITY,
+                              int8_range: -Float::INFINITY..0,
+                              float_range: -Float::INFINITY..Float::INFINITY)
+
+      record = PostgresqlRange.first
+
+      assert_equal(1...Float::INFINITY, record.int4_range)
+      assert_equal(-Float::INFINITY...1, record.int8_range)
+      assert_equal(-Float::INFINITY...Float::INFINITY, record.float_range)
+    end
+
     private
       def assert_equal_round_trip(range, attribute, value)
         round_trip(range, attribute, value)