[BUG] - Labels that are just numbers can't be imported

[JWittmeyer]

Describe the bug Uploading labels in numerical form results in an error on the import.

To Reproduce Steps to reproduce the behavior:

1. Go to new project
2. Select a file with labels as numbers (e.g. 1, 2, 3)
3. Upload file
4. See error

Expected behavior Labels are imported as "1", "2", "3"

Desktop (please complete the following information):

• OS: all
• Browser all
• Version 1.9.1

Additional context Example file with the issue example_numbered labels.zip

Example error log:

Traceback (most recent call last):
  File "/app/./api/transfer.py", line 70, in post
    init_file_import(task, project_id, is_global_update)
  File "/app/./api/transfer.py", line 236, in init_file_import
    transfer_manager.import_records_from_file(project_id, task)
  File "/app/./controller/transfer/manager.py", line 69, in import_records_from_file
    import_file(project_id, task)
  File "/app/./controller/transfer/record_transfer_manager.py", line 134, in import_file
    import_records_and_rlas(
  File "/app/./controller/transfer/record_transfer_manager.py", line 66, in import_records_and_rlas
    ) = split_record_data_and_label_data(chunk)
  File "/app/./controller/transfer/record_transfer_manager.py", line 270, in split_record_data_and_label_data
    item.strip() == ""
AttributeError: 'float' object has no attribute 'strip'

[jhoetter]

str(item) should (hopefully) do the trick :)

edit: didn't see your PR; go ahead with your solution :)