Python script to find large folders
ACCESS_ERROR_CODE is errno.EACCES.

BYTES_IN_GIGABYTE is clearer as 2**30. That's transparent enough that the constant and convert_bytes_to_gigabytes aren't needed, so I'd just write folder[1] / 2**30.

GIGABYTE_DISPLAY_LIMIT sounds like an upper limit to display. How about GIGABYTE_DISPLAY_THRESHOLD instead?

To reduce the opportunity for unit confusion, I'd keep the size and the threshold in bytes, and only convert to GB when printing.

You may want folder_sizes.sort(reverse=True) to get the largest ones first.

get_all_folder_sizes recurses over directories twice: once in os.walk and once in get_folder_size. This takes time quadratic in the tree depth, so it may be slow. Can you do the recursion just once, by returning a generator of (size, path) pairs, and recursing on subdirectories?

You can avoid the two try blocks by getting directory size in the same place as file size. (Then you don't even need isfile.)

The continue in the inner exception handler is redundant.