The 3rd cell of mtrl_finetuning_example_notebook_v3_prod.ipynb set
S3_TRAINING_DATA using an f-string that referenced an undefined STAGE
variable and an internal `-rftjob-input` bucket pattern left over from
when MTRL was tested in gamma/prod. Executing the cell raised
`NameError: name 'STAGE' is not defined`.
Replace it with a customer-facing placeholder S3 URI, consistent with
the convention used in the sibling sft_finetuning notebook, so users
(and the notebook test engine) can substitute their own dataset path.
Co-authored-by: hrehard <hrehard@amazon.com>
Hannah R.
b47a870284