[ci] skip NuGet creation

[StrikerRUS]

Hotfix after #6919.

Fixes the following error in master:

/usr/bin/bash --noprofile --norc /home/vsts/work/_temp/06cd32f1-a0bb-428f-811d-965de847e670.sh
Traceback (most recent call last):
  File "/home/vsts/work/1/s/.ci/create-nuget.py", line 20, in <module>
    copyfile(source / "lib_lightgbm.so", linux_folder_path / "lib_lightgbm.so")
  File "/usr/lib/python3.10/shutil.py", line 254, in copyfile
    with open(src, 'rb') as fsrc:
FileNotFoundError: [Errno 2] No such file or directory: '/home/vsts/work/1/s/binaries/PackageAssets/lib_lightgbm.so'

https://dev.azure.com/lightgbm-ci/lightgbm-ci/_build/results?buildId=17792&view=logs&j=1d2f55de-c984-5e06-0d18-75388f298a89&t=085f7f2b-f470-5c05-ab6d-e7d0f29f99ca&l=12

[jameslamb]

blegh sorry for missing this one, thank you. I hope we can resolve these issues soon.