s3:script: Avoid UnicodeDecodeError for samba-log-parser processing whole directory

s3:script: Avoid UnicodeDecodeError for samba-log-parser processing whole directory

When log directory contains zipped files like
old/log.rpcd_spoolss-20250831.gz we get error.
We want to ignore such files.

$ samba-log-parser --traceid 6 --merge-by-timestamp
Traceback (most recent call last):
  File "/usr/bin/samba-log-parser", line 382, in <module>
    main()
    ~~~~^^
  File "/usr/bin/samba-log-parser", line 311, in main
    process_file(
    ~~~~~~~~~~~~^
        record_list,
        ^^^^^^^^^^^^
    ...<3 lines>...
        options.traceid,
        ^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/bin/samba-log-parser", line 92, in process_file
    data = infile.readlines()
  File "<frozen codecs>", line 325, in decode
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x8b in position 1: invalid start byte

Signed-off-by: Pavel Filipenský <pfilipensky@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Autobuild-User(master): Pavel Filipensky <pfilipensky@samba.org>
Autobuild-Date(master): Tue Sep  9 13:50:00 UTC 2025 on atb-devel-224