[Bug] t.rast.import fails with ValueError

[landam]

Describe the bug
t.rast.import fails to import space-time dataset created by t.rast.export.

To Reproduce
Steps to reproduce the behavior:

1. Download sample dataset: sample.zip and unzip
2. Create new location (EPSG: 5514)
3. Run t.rast.import in=~/Downloads/sample.tar.bz2 output=sample
4. See error

Traceback (most recent call last):
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/scripts/t.rast.import", line 151, in <module>
    main()
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/scripts/t.rast.import", line 131, in main
    tgis.import_stds(
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/etc/python/grass/temporal/stds_import.py", line 583, in import_stds
    register_maps_in_space_time_dataset(
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/etc/python/grass/temporal/register.py", line 400, in register_maps_in_space_time_dataset
    assign_valid_time_to_map(
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/etc/python/grass/temporal/register.py", line 560, in assign_valid_time_to_map
    end_time = int(end)
               ^^^^^^^^
ValueError: invalid literal for int() with base 10: 'file'

Expected behavior
Space-time dataset imported successfully.

System description (please complete the following information):

• Operating System: Linux
• GRASS GIS version 8.4