Fix highlighting function return type annotation

syntax/python.vim

 syn region pythonFuncArgs    matchgroup=pythonFuncArgs    start='(' end=')' contained contains=pythonTypeAnno,@pythonExpression
 
 syn match pythonTypeAnno ":\s*\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*"hs=s+1 display contained contains=pythonType nextgroup=pythonTypeArgs
-syn match pythonTypeAnnoReturn "->\s*\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*:"hs=s+2,he=e-1 display contains=pythonType nextgroup=pythonTypeArgs
+syn match pythonTypeAnnoReturn "->\s*\%([^[:cntrl:][:space:][:punct:][:digit:]]\|_\)\%([^[:cntrl:][:punct:][:space:]]\|_\)*"hs=s+2,he=e-1 display contains=pythonType nextgroup=pythonTypeArgs
 syn region pythonTypeArgs matchgroup=pythonTypeArgs start='\[' end='\]' display contained contains=pythonType,pythonTypeArgs
 syn keyword pythonType Any AnyStr Callable ClassVar Tuple Union Optional Type TypeVar None contained
 syn keyword pythonType AbstractSet MutableSet Mapping MutableMapping Sequence MutableSequence ByteString Deque List contained