[issue#12603][FIX] invoice_xunnel: Search invoice related to credit note
Invoice with uuid
Credit note that contains in the
<cfdi:CfdiRelacionado UUID="6a8f9b60-2b51-4f05-93b4-8bc418c3166c"/> (lowercased)
When importing the xml of the credit note, does not get the related invoice, because it does not compare upper and lower case for uuid.
This fix changes the uuid of the invoices found to lowercase and the uuid of the XML of the credit note to lowercase, to compare them.