Idempotency issue with dollar-quoted strings since version 5.10

[thunze]

Using the latest version 5.10, formatting

SELECT results_eq(
  $$ SELECT * FROM some_table WHERE a = 'b' $$,
  $$ VALUES (1, 2, 3) $$
);

results in

SELECT
    results_eq ($$
        SELECT
            * FROM some_table
            WHERE
                a = 'b' $$, $$
            VALUES (1, 2, 3) $$);

Formatting again adds a space:

-                a = 'b' $$, $$
+                a = 'b'  $$, $$

Formatting again adds another space:

-                a = 'b'  $$, $$
+                a = 'b'   $$, $$

I.e., the formatting doesn't "converge".