You're elongating vowels etc. when you sing. If you sing in English you're most likely going to sound like every other English singer.

The only way you don't is if you purposely slow down your singing make it sound like your talking accent. This works with some genres (e.g. rap) but not others.

a very long time. Jeff Lynne, who has a strong Birmingham accent, sang a lot of ELO’s songs in the 70s and 80s with a noticeable American accent. Sweet Is The Night being a prime example