Upsert fails after update_schema().union_by_name() due to schema mismatch

### Apache Iceberg version

0.10.0

### Please describe the bug 🐞

When performing an `upsert` operation after adding a new column via `update_schema().union_by_name()` , the operation fails with a ValueError indicating that the schema field names don't match.

**To reproduce**:
```python
from pyiceberg.catalog import load_catalog
import polars as pl

catalog = load_catalog("default", **{"type": "in-memory"})

df = pl.DataFrame(
[
{"id": 1, "name": "Alice", "age": 30, "city": "São Paulo"},
{"id": 2, "name": "Bob", "age": 25, "city": "Rio de Janeiro"},
{"id": 3, "name": "Carol", "age": 35, "city": "Belo Horizonte"},
{"id": 4, "name": "David", "age": 28, "city": "Curitiba"},
]
)

arrow = df.to_arrow()

catalog.create_namespace_if_not_exists("default")
catalog.create_table_if_not_exists("default.my_table", arrow.schema)
table = catalog.load_table("default.my_table")

try:
table.append(arrow)

# Add a new column
arrow = df.with_columns(ping=pl.lit("pong")).to_arrow()

# Update schema to include the new column
with table.update_schema() as update_schema:
update_schema.union_by_name(arrow.schema)
table = table.refresh()

# This fails with ValueError
table.upsert(arrow, ["id"])
finally:
catalog.drop_table("default.my_table")
```

**Error:**
`ValueError: Target schema's field names are not matching the table's field names: ['id', 'name', 'age', 'city', 'ping'], ['id', 'name', 'age', 'city']`

**Stack trace:**
```
File "pyiceberg/table/__init__.py", line 1343, in upsert
return tx.upsert(
File "pyiceberg/table/__init__.py", line 825, in upsert
rows_to_update = upsert_util.get_rows_to_update(df, rows, join_cols)
File "pyiceberg/table/upsert_util.py", line 92, in get_rows_to_update
source_table.cast(target_table.schema)
File "pyarrow/table.pxi", line 4721, in pyarrow.lib.Table.cast
```

**Expected:**
The upsert operation should succeed after the schema has been updated to include the new column.

### Willingness to contribute

- [ ] I can contribute a fix for this bug independently
- [x] I would be willing to contribute a fix for this bug with guidance from the Iceberg community
- [ ] I cannot contribute a fix for this bug at this time

pyiceberg/table/upsert_util.py の get_rows_to_update から始め、続いて pyiceberg/table/__init__.py の table.upsert パスと、失敗している pyarrow Table.cast 呼び出しを追ってください。提供された再現コードをバージョン 0.10.0 に対して実行し、union_by_name が ping を追加した後も upsert が成功し、更新されたスキーマが保持されることを示すリグレッションテストのカバレッジを追加してください。

索引モデルが issue の本文から書いたものです。