[dev-context] allow non-ASCII chars in scite-xml

Hans, here is a patch, copied from buff-imp-xml.lua, so that XML elements are highlighted when they contain non-ASCII chars. MWE that shows the issue (commenting the first line gives different results): \usemodule[scite] \starttext \startTEXpage[offset=1ex] \type[option=xml]{<ans/>} \type[option=xml]{} \stopTEXpage \stoptext Many thanks for your help, Pablo