Using scan_csv with with_column_names argument disables schema validation

[hotaru355]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

Given the following CSV file:

col1
notAnInt

This query should raise an exception, as the col1 column is not a pl.Int16.

pl.scan_csv(
    "test.csv",
    schema={"col1": pl.Int16},
    with_column_names=lambda names: names,
).sink_csv("out1.csv")

Log output

RUN STREAMING PIPELINE
[csv -> parquet_sink]
STREAMING CHUNK SIZE: 50000 rows

Issue description

When using the scan_csv query with the with_column_names argument, any schema validation enforced by the schema argument is disabled. Simply removing the with_column_names argument from the query enables validation again.

Expected behavior

This query should raise an exception just as it does when omitting the with_column_names argument:

polars.exceptions.ComputeError: could not parse `notAnInt` as dtype `i16` at column 'col1' (column number 1)

Installed versions

--------Version info---------
Polars:               1.0.0
Index type:           UInt32
Platform:             Linux-6.9.3-76060903-generic-x86_64-with-glibc2.35
Python:               3.11.7 (main, Feb 12 2024, 10:41:42) [GCC 11.4.0]

----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          <not installed>
connectorx:           <not installed>
deltalake:            <not installed>
fastexcel:            <not installed>
fsspec:               <not installed>
gevent:               <not installed>
great_tables:         <not installed>
hvplot:               <not installed>
matplotlib:           3.7.5
nest_asyncio:         <not installed>
numpy:                1.26.4
openpyxl:             <not installed>
pandas:               <not installed>
pyarrow:              <not installed>
pydantic:             1.10.15
pyiceberg:            <not installed>
sqlalchemy:           <not installed>
torch:                <not installed>
xlsx2csv:             <not installed>
xlsxwriter:           <not installed>