assignments with ':=' when the variable has only been declared

corpus/plpgsql/block.txt

@@ -147,6 +147,7 @@ DO $$
 BEGIN
     SELECT 1;
     foo.bar = lower(foo.baz);
+    foo.bar := lower(foo.baz);
     RETURN 2;
 END
 $$;
@@ -165,6 +166,11 @@ $$;
           (function_call
             (identifier)
             (identifier)))
+        (assign_statement
+          (identifier)
+          (function_call
+            (identifier)
+            (identifier)))
         (return_statement
           (number)))
       (dollar_quote))))

grammar.js

@@ -459,7 +459,7 @@ module.exports = grammar({
       optional($.execute_using),
     ),
     execute_using: $ => seq(kw("using"), commaSep1($._value_expression)),
-    assign_statement: $ => seq($.identifier, "=", $._value_expression),
+    assign_statement: $ => seq($.identifier, choice("=", ":="), $._value_expression),
     return_statement: $ => seq(kw("return"), choice(
       seq(kw("query"), $.select_statement),
       seq(kw("query"), $.execute_statement),