Upsert with None values fails on "Invalid literal value: None"

### Apache Iceberg version

main (development)

### Please describe the bug 🐞

Upserting a table fails when the input dataframe contains `None` in a join column.

I've reproduced this error by editing `test_upsert_with_nulls` from #1861, adding this at the end:

```python
# upsert table with null value
data_with_null = pa.Table.from_pylist(
[
{"foo": None, "bar": 1, "baz": False},
],
schema=schema,
)
upd = table.upsert(data_with_null, join_cols=["foo"])
```

The `foo` column contains `None`, causing `TypeError: Invalid literal value: None`.

```
tests/table/test_upsert.py:720: in test_upsert_with_nulls
upd = table.upsert(data_with_null, join_cols=["foo"])
pyiceberg/table/__init__.py:1343: in upsert
return tx.upsert(
pyiceberg/table/__init__.py:798: in upsert
matched_predicate = upsert_util.create_match_filter(df, join_cols)
pyiceberg/table/upsert_util.py:37: in create_match_filter
return In(join_cols[0], unique_keys[0].to_pylist())
pyiceberg/expressions/__init__.py:682: in __new__
literals_set: Set[Literal[L]] = _to_literal_set(literals)
pyiceberg/expressions/__init__.py:52: in _to_literal_set
return {_to_literal(v) for v in values}
pyiceberg/expressions/__init__.py:52: in
return {_to_literal(v) for v in values}
pyiceberg/expressions/__init__.py:59: in _to_literal
return literal(value)
pyiceberg/expressions/literals.py:159: in literal
raise TypeError(f"Invalid literal value: {repr(value)}")
E TypeError: Invalid literal value: None
```

### 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

Inizia da tests/table/test_upsert.py, in particolare test_upsert_with_nulls e la riproduzione aggiunta, poi leggi pyiceberg/table/upsert_util.py:create_match_filter e la gestione dei valori letterali delle espressioni mostrata nel traceback. Conferma con la community il comportamento previsto per un valore null nella colonna di join, quindi fai funzionare il caso di upsert e aggiungi o aggiorna un test di regressione che passi.

Scritto dal modello di indicizzazione a partire dal testo della issue.