that bolt is constantly heating and cooling...
now what did we learn about this in science class

anyway, i would take all remaining parts off to make room to work, then i would use a handheld cutting wheel or grinder to notch the end of the bolt to try to get it out

did it snap off inside the bracket, as in the remaining bolt stud is not visible? this will make it much more difficult to remove, and you may have to cut the bracket on the open bolt hole with a cutting wheel and then split it off, and then notch the bolt, remove it, and buy a new bracket and bolts. here

TAKE A PICTURE

~boomer