### Godot version

v4.0.rc1.official [8843d9ad3]

### System information

Lubuntu

### Issue description

You can't use + or += to mutate typed arrays.

It seems to be not correctly getting the type information from the second operand.

An erudite poster on the discord puts it differently:
> it's more like operator + doesn't retain Array typing
> the syntax for Array Concatenation via operators, but the idea gets across i think


The error you see is:
```Trying to assign an array of type "Array" to a variable of type "Array[int]".```


### Steps to reproduce

```
	var Alice: Array[int] = [1,2,3]
	var Bob: Array[int] = [4,5,6]
	Alice += Bob
```
This will crash with the above error message.

### Minimal reproduction project

[plus_syntax_broken_demo_project.zip](https://github.com/godotengine/godot/files/10694514/plus_syntax_broken_demo_project.zip)

downgrades_assigned = !assigned_is_hard;
		}
	}
	p_assignment->set_datatype(op_type);
	if (assignee_is_variant) {
		if (!assignee_is_hard) {
			
			mark_node_unsafe(p_assignment);
		}
	} else {
		if (assignee_is_hard && !assigned_is_hard) {
			
			mark_node_unsafe(p_assignment);
			p_assignment->use_conversion_assign = true;
			downgrades_assigned = downgrades_assigned || (!assigned_is_variant && !is_type_compatible(assignee_type, op_type, true, p_assignment->assigned_value));
		} else if (compatible) {
			if (op_type.is_variant()) {
				
				mark_node_unsafe(p_assignment);
				if (assignee_is_hard) {
					
					p_assignment->use_conversion_assign = true;
				} else {
					
					downgrades_assignee = true;
				}
			} else if (!is_type_compatible(assignee_type, op_type, assignee_is_hard, p_assignment->assigned_value)) {
				
				mark_node_unsafe(p_assignment);
				if (assignee_is_hard) {