Fix "tests: ido: rework test for option -P"

The Github Actions FreeBSD-vm, NetBSD-vm and OpenBSD-vm run the CI as
root.

The test prepends the hardcoded value of root (i.e. 0) to the list of
the expected GROUPS.

That value is already part of the GROUPS since ido does not "switch" to
another user (i.e. it runs as root and it usurps the root identity).

As a consequence, the root user-id is duplicated and raises the error
attached below.

This fixes commit 657c1be.

Fixes:

	Running ido: test option -P preserves group vector 0 0 0 5...
	GROUPS=0 0 5
	ido: test option -P preserves group vector 0 0 0 5: [KO]

tests/tests-ido.bash

@@ -357,14 +357,26 @@ else
 fi
 echo
 
-run "ido: test option -P preserves group vector 0 ${GROUPS[*]}"
-if ( export SHELL=bash && ido -P -s <<<'echo "GROUPS=${GROUPS[*]}"' | tee /dev/stderr | grep -q "^GROUPS=0 ${GROUPS[*]}$" )
+if [[ "$UID" -eq 0 ]]
 then
-	ok
+	run "ido: test option -P preserves group vector ${GROUPS[*]}"
+	if ( export SHELL=bash && ido -P -s <<<'echo "GROUPS=${GROUPS[*]}"' | tee /dev/stderr | grep -q "^GROUPS=${GROUPS[*]}$" )
+	then
+		ok
+	else
+		ko
+	fi
+	echo
 else
-	ko
+	run "ido: test option -P preserves group vector 0 ${GROUPS[*]}"
+	if ( export SHELL=bash && ido -P -s <<<'echo "GROUPS=${GROUPS[*]}"' | tee /dev/stderr | grep -q "^GROUPS=0 ${GROUPS[*]}$" )
+	then
+		ok
+	else
+		ko
+	fi
+	echo
 fi
-echo
 
 run "ido: test option --preserve-groups preserves group vector ${GROUPS[*]}"
 if ( export SHELL=bash && ido --user="$USER" --preserve-groups --shell <<<'echo "GROUPS=${GROUPS[*]}"' | tee /dev/stderr | grep -q "GROUPS=${GROUPS[*]}" )