Don't validate non dirty association targets

Fixes #36581.

This fixes an issue where validations would return differently when a previously saved invalid association was loaded between calls:

    assert_equal true, squeak.valid?
    assert_equal true, squeak.mouse.present?
    assert_equal true, squeak.valid?

Here the second assert would return

    Expected: true
    Actual: false

Limiting validations to associations that would be normally saved (using autosave: true) due to changes means that loading invalid associated relations will not change the return value of the parent relations's `valid?` method.

1 files changed, 8 insertions, 0 deletions

diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index b6c0ae0de2..dd0ff759b6 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -563,6 +563,10 @@ ActiveRecord::Schema.define do
     t.string   :type
   end
 
+  create_table :mice, force: true do |t|
+    t.string   :name
+  end
+
   create_table :movies, force: true, id: false do |t|
     t.primary_key :movieid
     t.string      :name
@@ -843,6 +847,10 @@ ActiveRecord::Schema.define do
     end
   end
 
+  create_table :squeaks, force: true do |t|
+    t.integer :mouse_id
+  end
+
   create_table :prisoners, force: true do |t|
     t.belongs_to :ship
   end