### Godot version

v4.0.2.stable.custom_build (nixpkgs version)

### System information

NixOS

### Issue description

The [docs](https://docs.godotengine.org/en/latest/tutorials/scripting/gdscript/gdscript_basics.html#variables) seem to specify that uninitialized variables are null (as noted in this comment on the related issue: https://github.com/godotengine/godot/issues/56223#issuecomment-1175794500):
`var a # Data type is 'null' by default.`

This isn't always the case inside branches within loops. Instead, the variables can take on values from other branches.

### Related
- https://github.com/godotengine/godot/issues/56223

### Steps to reproduce

```
@tool
extends EditorScript

func _run():
	for i in 5:
		if i % 2:
			var j = i
			print("i = %s, j = %s" % [i, j])
		else:
			var k
			print("i = %s, k = %s" % [i, k])
```

Running this prints:
```
i = 0, k = <null>
i = 1, j = 1
i = 2, k = 1
i = 3, j = 3
i = 4, k = 3
```

This version also gives the exact same result:
```
@tool
extends EditorScript

func _run():
	for i in 5:
		match i % 2:
			1:
				var j = i
				print("i = %s, j = %s" % [i, j])
			0:
				var k
				print("i = %s, k = %s" % [i, k])
```

In addition, behavior similar to that described in https://github.com/godotengine/godot/issues/56223#issuecomment-1000996579 can still be reproduced as follows:
```
@tool
extends EditorScript

func _run():
	for i in 3:
		if i % 2:
			for j in range(1, 6, 3):
				pass
			print("i = %s" % i)
		else:
			var k
			var l
			var m
			print("i = %s, k = %s, l = %s, m = %s" % [i, k, l, m])
```
Which prints:
```
i = 0, k = <null>, l = <null>, m = <null>
i = 1
i = 2, k = 4, l = 7, m = (1, 6, 3)
```

### Minimal reproduction project

N/A
ERR_FAIL_COND_V_MSG(p_node->type != Node::FUNCTION, false, vformat(R"("%s" annotation can only be applied to functions.)", p_annotation->name));
	FunctionNode *function = static_cast<FunctionNode *>(p_node);
	if (function->rpc_config.get_type() != Variant::NIL) {
		push_error(R"(RPC annotations can only be used once per function.)", p_annotation);
		return false;
	}
	Dictionary rpc_config;
	rpc_config["rpc_mode"] = MultiplayerAPI::RPC_MODE_AUTHORITY;
	if (!p_annotation->resolved_arguments.is_empty()) {
		unsigned char locality_args = 0;
		unsigned char permission_args = 0;
		unsigned char transfer_mode_args = 0;
		for (int i = 0; i < p_annotation->resolved_arguments.size(); i++) {
			if (i == 3) {
				rpc_config["channel"] = p_annotation->resolved_arguments[i].operator int();
				continue;
			}
			String arg = p_annotation->resolved_arguments[i].operator String();
			if (arg == "call_local") {
				locality_args++;
				rpc_config["call_local"] = true;
			} else if (arg == "call_remote") {
				locality_args++;
				rpc_config["call_local"] = false;
			} else if (arg == "any_peer") {