I assume that the type GIT_BRANCHis String, while it "support/${version}"is GString. If you convert the latter to String, it should work:
def version = "1.2"
switch(GIT_BRANCH) {
case "develop":
result = "dev"
break
case ["master", "support/${version}".toString()]:
result = "list"
break
case "support/${version}":
result = "sup"
break
default:
result = "def"
break
}
echo "${result}"
, , . GString List.