Fix fd dup tests to be more robust

i.e. not depending on the first fd to be 4.
5 jobs for fd-dup-test-robusty in 6 minutes and 11 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #23660
build:linux

00:06:11

failed #23661
build:redox

00:05:58

 
  Test
skipped #23664
allowed to fail
fmt
skipped #23662
test:linux
skipped #23663
test:redox
 
Name Stage Failure
failed
build:redox Build
src/header/sys_wait
src/header/termios
src/header/time
src/header/unistd
src/header/utime
src/header/wchar
mv "target/x86_64-unknown-redox"/include.partial "target/x86_64-unknown-redox"/include
touch "target/x86_64-unknown-redox"/include
ERROR: Job failed: exit code 1