Replacing basename with nemo specific filename variable %N

[freckhard]

This change replaces the shell-based filename extraction using basename %F with Nemo's native %N filename variable. This simplifies the command, avoids shell quoting issues, and improves reliability.

[rcalixte]

cc @torchipeppo

[torchipeppo]

Well, TIL :)
I just made a quick test and it appears to be in order.
Actually, I got curious and found the Nemo wiki on GitHub where it says that %N is deprecated and the same as %f (lowercase): is this important enough to warrant a correction?
Source: https://github.com/linuxmint/nemo/wiki/Actions-Quick-Reference

[torchipeppo]

Did a test with %f the other day and it seems to work just the same, even a quick search in the nemo source code [1] [2] shows they're treated exactly the same.

At this point @rcalixte I'd prefer to avoid what's been marked as deprecated, either by applying this change now or by approving this PR as is and fixing later.

Otherwise @freckhard thank you very much for the thought and the idea! ^_^