expand: fix duplicate flags

[allaboutevemirolive]

Fixed expand failed when executing multiple args. See #5671

GNU:

$ echo -e "foo\tbar" | expand -i -i
foo	bar

Current uutils/coreutils:

$ echo -e "foo\tbar" | uuu expand -i -i
error: the argument '--initial' cannot be used multiple times

Usage: /home/nemesis/Documents/Github/Focus/util/coreutils/target/debug/coreutils expand [OPTION]... [FILE]...

For more information, try '--help'.

Expected behavior for uutils/coreutils:

$ echo -e "foo\tbar" | uuu expand -i -i
foo	bar

[cakebaker]

The change itself looks good. With the test, I think it is a bit of an overkill to introduce an additional fixture and you could simply use the fixture used in test_with_trailing_tab_i.

[allaboutevemirolive]

@cakebaker Do you know why the GNU test failed? Or should I run cargo test on my machine again? :)

[sylvestre]

Just ignore it :)