Apex domains cannot have CNAME records.
Question and response
Question
dig srv.celeste.fr. NS
Answer
srv.celeste.fr. 5 NS ns2.celeste.fr.
srv.celeste.fr. 5 NS ns1.celeste.fr.
srv.celeste.fr. 5 NS ns3.celeste.fr.
Authority
The response has no authority records.
Additional
ns1.celeste.fr. 5 A 83.142.144.247
ns2.celeste.fr. 5 A 163.172.72.108
ns3.celeste.fr. 5 A 83.142.144.248
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0