fix(postgres): Fix exp.WidthBucket required args

Author: VaggelisD

sqlglot/expressions.py

@@ -8279,7 +8279,7 @@ class Skewness(AggFunc):
 
 
 class WidthBucket(Func):
-    arg_types = {"this": True, "min_value": True, "max_value": True, "num_buckets": True}
+    arg_types = {"this": True, "min_value": True, "max_value": False, "num_buckets": False}
 
 
 class CovarSamp(Binary, AggFunc):

tests/dialects/test_postgres.py

@@ -1015,6 +1015,8 @@ def test_postgres(self):
             "SELECT SLOPE(point '(4,4)', point '(0,0)')",
             "SELECT SLOPE(CAST('(4,4)' AS POINT), CAST('(0,0)' AS POINT))",
         )
+        self.validate_identity("SELECT WIDTH_BUCKET(10, ARRAY[5, 15])")
+        self.validate_identity("SELECT WIDTH_BUCKET(10, 5, 15, 25)")
 
     def test_ddl(self):
         # Checks that user-defined types are parsed into DataType instead of Identifier