BUG #18142: strange behaviour of "UPDATE" with id_encode()

The following bug has been logged on the website:

Bug reference:      18142
Logged by:          DataSelfService Srl
Email address:      info@dataselfservice.com
PostgreSQL version: 15.4
Operating system:   docker
Description:

Hi,

In short: why is `UPDATE...id_encode()` missbehaving and behaving
differently in case a single `SET` or multiple `SET` on the same line are
done?

Details

I'm running a kubernetes instance of  `15.4-alpine3.18`, with modified image
`IMG_POSTGRES_TAG` added with `pg_hashids` via following `Dockerfile`:
```
FROM postgres:15.4-alpine3.18


       
 
RUN apk add --no-cache --virtual .build-deps build-base postgresql-dev
clang15 llvm15 ; \
    wget -qO-
https://github.com/iCyberon/pg_hashids/archive/refs/tags/v1.2.1.tar.gz | tar
xzf - -C /tmp && \
    make -C /tmp/pg_hashids-1.2.1 && \
    make -C /tmp/pg_hashids-1.2.1 install && \
    rm -rf /tmp/pg_hashids-1.2.1 && \
    apk del .build-deps
```
Deployed to the cluster with:
```
helm install postgres --set

image.repository=postgres,image.tag=${IMG_POSTGRES_TAG},primary.service.clusterIP=${POSTGRES_CLUSTER_IP},primary.persistence.existingClaim=postgres
oci://registry-1.docker.io/bitnamicharts/postgresql
```

The issue is that a trigger function which generates hashes during insert,
miss-behaves and generates a *wrong hash ending with a space*. 

Reproduce it by running the following SQL: 
```
BEGIN;
DROP SCHEMA IF EXISTS test CASCADE;
CREATE SCHEMA test;
CREATE TABLE test.test (
    id bigint NOT NULL,
    data text,
    ids text,
    ids1 text,
    ids2 text
);
CREATE SEQUENCE test.test_id_seq
    START WITH 1
    INCREMENT BY 1
    NO MINVALUE
    NO MAXVALUE
    CACHE 1;
ALTER SEQUENCE test.test_id_seq OWNED BY test.test.id;
ALTER TABLE ONLY test.test
    ALTER COLUMN id SET DEFAULT nextval('test.test_id_seq'::regclass);
CREATE FUNCTION test.myfunc ()
    RETURNS TRIGGER
    LANGUAGE plpgsql
    AS $$
BEGIN
    UPDATE
        test.test
    SET
        ids = id_encode (NEW.id, 'hash1', 5,
'abcdefghijklmnopqrstuvwxyz'),
        ids1 = id_encode (NEW.id, 'hash2', 12,
'abcdefghijklmnopqrstuvwxyz'),
        ids2 = id_encode (NEW.id, 'hash3', 12,
'abcdefghijklmnopqrstuvwxyz')
    WHERE
        id = NEW.id;
    RETURN new;
END;
$$;
CREATE FUNCTION test.myfunc_fix ()
    RETURNS TRIGGER
    LANGUAGE plpgsql
    AS $$
BEGIN
    UPDATE
        test.test
    SET
        ids = id_encode (NEW.id, 'hash1', 5, 'abcdefghijklmnopqrstuvwxyz')
    WHERE
        id = NEW.id;
    UPDATE
        test.test
    SET
        ids1 = id_encode (NEW.id, 'hash2', 12,
'abcdefghijklmnopqrstuvwxyz'),
        ids2 = id_encode (NEW.id, 'hash3', 12,
'abcdefghijklmnopqrstuvwxyz')
    WHERE
        id = NEW.id;
    RETURN new;
END;
$$;
CREATE TRIGGER test_myfunc
    AFTER INSERT ON test.test
    FOR EACH ROW
    EXECUTE FUNCTION test.myfunc ();
\copy test.test to stdout CSV FORCE QUOTE *;
INSERT INTO test.test (data)
    VALUES ('a'),
    ('b');
\copy test.test to stdout CSV FORCE QUOTE *;
DROP TRIGGER test_myfunc ON test.test;
CREATE TRIGGER test_myfunc_fix
    AFTER INSERT ON test.test
    FOR EACH ROW
    EXECUTE FUNCTION test.myfunc_fix ();
\copy test.test to stdout CSV FORCE QUOTE *;
INSERT INTO test.test (data)
    VALUES ('a1'),
    ('b1');
\copy test.test to stdout CSV FORCE QUOTE *;
COMMIT
```

Run it with: `cat test.sql | psq -U testdb`.

Output looks like:
```
WARNING:  database "testdb" has no actual collation version, but a version
was recorded
BEGIN
NOTICE:  drop cascades to 3 other objects
DETAIL:  drop cascades to table test.test
drop cascades to function test.myfunc()
drop cascades to function test.myfunc_fix()
DROP SCHEMA
CREATE SCHEMA
CREATE TABLE
CREATE SEQUENCE
ALTER SEQUENCE
ALTER TABLE
CREATE FUNCTION
CREATE FUNCTION
CREATE TRIGGER
INSERT 0 2
"1","a","zmnb ","wzejgmprmnpa","yzvmbrydnogd"
"2","b","pylw ","xabdomywmenl","zmbexnawnpaq"
DROP TRIGGER
CREATE TRIGGER
"1","a","zmnb ","wzejgmprmnpa","yzvmbrydnogd"
"2","b","pylw ","xabdomywmenl","zmbexnawnpaq"
INSERT 0 2
"1","a","zmnb ","wzejgmprmnpa","yzvmbrydnogd"
"2","b","pylw ","xabdomywmenl","zmbexnawnpaq"
"3","a1","zmpdm","jlyezmrwvakd","ybjwprgzndxl"
"4","b1","dmepy","ydqlpvjrvxnz","jwmvprxmnkea"
COMMIT
```

The issue is the space in the end of "zmnb ". Utilizing `myfunc_fix()` which
basically runs separated `UPDATE`, works i.e. generates hashes without the
trailing  space. But I am not at all satisfied and I would like to
understand what is the root cause?!?! 

I noticed the `WARNING:  database "testdb" has no actual collation version,
but a version was recorded` and I am not sure how that is realted (I do not
really know what is the impact of that. 

Any help or ideas?