Wrong result from index lookup on CHAR(n) when a longer constant is equal under a collation with expansions

  SET NAMES utf8mb4;

  CREATE TABLE t1 (v CHAR(1) COLLATE utf8mb4_german2_ci, KEY(v));

  INSERT INTO t1 VALUES ('ß'),('s'),('x');

  SELECT v FROM t1 WHERE v = 'ss';

  DROP TABLE t1;

  CREATE COLLATION de_ss (provider = icu, locale = 'de-u-ks-level1',

                          deterministic = false);

  CREATE TABLE t1 (v char(1) COLLATE de_ss);

  CREATE INDEX ON t1 (v);

  INSERT INTO t1 VALUES ('ß'), ('s'), ('x');

  SET enable_seqscan = off;

  SELECT v FROM t1 WHERE v = 'ss';

  DROP TABLE t1;

  DROP COLLATION de_ss;