Fix duplicate indices in ExprIndices (SkriptLang#8343)

Co-authored-by: sovdee <10354869+sovdeeth@users.noreply.github.com>

Author: UnderscoreTud

src/main/java/ch/njol/skript/expressions/ExprIndices.java

@@ -91,7 +91,7 @@ public boolean init(Expression<?>[] exprs, int matchedPattern, Kleenean isDelaye
 			if (separator != -1)
 				keys[i] = keys[i].substring(0, keys[i].indexOf(Variable.SEPARATOR));
 		}
-		return keys;
+		return Arrays.stream(keys).distinct().toArray(String[]::new);
 	}
 
 	@Override

src/test/skript/tests/syntaxes/expressions/ExprIndices.sk

@@ -1,3 +1,11 @@
+test "indices":
+	set {_list::a} to 1
+	set {_list::b} to 2
+	set {_list::c::e} to 3
+	set {_list::c::f} to 4
+	assert size of indices of {_list::*} is 3
+	assert indices of {_list::*} is "a", "b" and "c"
+
 test "sorted indices":
 	assert indices of {single-var} is set to fail with "Should not be able to acquire indices of anything other than a list"
 	assert indices of wooden hoe is set to fail with "Should not be able to acquire indices of anything other than a list"