[st] fix declaration of ST_DWITHIN (closes #17100018)

cubicweb_postgis/site_cubicweb.py

@@ -135,10 +135,10 @@ class ST_CONTAINS(FunctionDescr):
 
 
 class ST_DWITHIN(FunctionDescr):
-    minargs = 2
-    maxargs = 2
+    minargs = 3
+    maxargs = 4
     supported_backends = ('postgres',)
-    rtype = 'Float'
+    rtype = 'Bool'
 
 
 class ST_LENGTH(FunctionDescr):