[Bug] aggregate function in partial update inconsistency

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/paimon/issues) and found nothing similar.

### Paimon version

1.0.0

### Compute Engine

Flink

### Minimal reproduce step

CREATE TABLE t1
(
k INT,
a INT,
b INT,
g_1 INT,
PRIMARY KEY (k) NOT ENFORCED
) WITH (
'merge-engine' = 'partial-update',
'fields.a.aggregate-function' = 'sum',
'fields.b.aggregate-function' = 'last_non_null_value',
'fields.g_1.sequence-group' = 'a,b'
);

INSERT INTO t1 VALUES (1, 1, 1, 1);
INSERT INTO t1 VALUES (1, 2, 2, 2);
INSERT INTO t1 VALUES (1, 3, 3, 1);

### What doesn't meet your expectations?

when g_1 of third record is smaller, third record should be ignored。
I expect the result to be: 1,3,2,2

### Anything else?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start with the SQL reproduction for table t1 using partial-update, the sum and last_non_null_value aggregate functions, and sequence group a,b; run it with Paimon 1.0.0 on Flink and compare the third update with the expected result 1,3,2,2. Trace the partial-update handling to determine why a lower g_1 does not cause that record to be ignored, then add regression coverage for this case.

Written by the indexing model from the issue text.