[FIX] base_import: prevent traceback of Unsupported file format text/csv

When we try to import bank statement CSV file with all required columns and
set the encoding format as koir8_r we get (ValueError: Unsupported file format
text/csv, import only supports CSV, ODS, XLS and XLSX) this error.

steps to reproduce:
    1. Go to accounting and then import bank statement.
    2. Select a csv file to import with all required columns.
    3. Set Encoding format as koir8_r and then click on 'TEST' or 'IMPORT'.
    4. The error will occur.

see this traceback: https://tinyurl.com/24bxk7bt



Applying this commit will fix this issue.

sentry-4049996747

closes odoo/odoo#118615

Signed-off-by: Achraf <abz@odoo.com>