[GDScript] Fix incorrect compound assignment

Reverts in-place compound assignments

Added test to ensure correctness

modules/gdscript/tests/scripts/runtime/features/assign_operator.gd

@@ -0,0 +1,31 @@
+# https://github.com/godotengine/godot/issues/75832
+
+@warning_ignore("narrowing_conversion")
+func test():
+	var hf := 2.0
+	var sf = 2.0
+
+	var i := 2
+	i *= hf
+	i *= sf
+	i *= 2.0
+	print(i)
+	var v2 := Vector2i(1, 2)
+	v2 *= hf
+	v2 *= sf
+	v2 *= 2.0
+	print(v2)
+	var v3 := Vector3i(1, 2, 3)
+	v3 *= hf
+	v3 *= sf
+	v3 *= 2.0
+	print(v3)
+	var v4 := Vector4i(1, 2, 3, 4)
+	v4 *= hf
+	v4 *= sf
+	v4 *= 2.0
+	print(v4)
+
+	var arr := [1, 2, 3]
+	arr += [4, 5]
+	print(arr)