Prevent invalid code when using dynamic finders with Ruby's reserved words.

The dynamic finder was creating the method signature with the parameters name,
which may have reserved words and this way creating invalid Ruby code.

Closes: #13261

    Example:

        # Before
        Dog.find_by_alias('dog name')

        # Was creating this method
        def self.find_by_alias(alias, options = {})

        # After
        Dog.find_by_alias('dog name')

        # Will create this method
        def self.find_by_alias(_alias, options = {})