feat: Gem::Specification#initialize_copy deep-copies requirements

to avoid accidentally mutating the original's state when doing:

```ruby
spec2 = spec.dup
spec2.required_rubygems_version.concat([">= 3.3.22"])
```

see rake-compiler/rake-compiler#236 for a
real-world use case that would be made simpler with this behavior.

lib/rubygems/specification.rb

@@ -2075,7 +2075,8 @@ def initialize(name = nil, version = nil)
   end
 
   ##
-  # Duplicates array_attributes from +other_spec+ so state isn't shared.
+  # Duplicates Array and Gem::Requirement attributes from +other_spec+ so state isn't shared.
+  #
 
   def initialize_copy(other_spec)
     self.class.array_attributes.each do |name|
@@ -2097,6 +2098,9 @@ def initialize_copy(other_spec)
         raise e
       end
     end
+
+    @required_ruby_version = other_spec.required_ruby_version.dup
+    @required_rubygems_version = other_spec.required_rubygems_version.dup
   end
 
   def base_dir

test/rubygems/test_gem_specification.rb

@@ -1194,10 +1194,13 @@ def test_initialize_copy
     assert_same spec.bindir, dup_spec.bindir
 
     assert_equal ">= 0", spec.required_ruby_version.to_s
-    assert_same spec.required_ruby_version, dup_spec.required_ruby_version
+    assert_equal spec.required_ruby_version, dup_spec.required_ruby_version
+    refute_same spec.required_ruby_version, dup_spec.required_ruby_version
 
     assert_equal ">= 0", spec.required_rubygems_version.to_s
-    assert_same spec.required_rubygems_version,
+    assert_equal spec.required_rubygems_version,
+                 dup_spec.required_rubygems_version
+    refute_same spec.required_rubygems_version,
                 dup_spec.required_rubygems_version
   end