assigning '0.0' to a nullable numeric column does not make it dirty
Merge pull request #9042 from senny/9034_float_0_0_is_always_dirty

Assigning '0.0' to a nullable numeric column does not make it dirty

Example:
    product = Product.create price: 0.0
    product.price = '0.0'
    product.changed? # => false (this used to return true)
    product.changes # => {} (this used to return { price: [0.0, 0.0] })