### 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
if (p_annotation->name == SNAME("@export_range")) {
		if (export_type.builtin_type == Variant::INT) {
			variable->export_info.type = Variant::INT;
		}
	}
	if (p_annotation->name == SNAME("@export_multiline")) {
		if (export_type.builtin_type == Variant::ARRAY && export_type.has_container_element_type()) {
			DataType inner_type = export_type.get_container_element_type();
			if (inner_type.builtin_type != Variant::STRING) {
				push_error(vformat(R"("%s" annotation on arrays requires a string type but type "%s" was given instead.)", p_annotation->name.operator String(), inner_type.to_string()), variable);
				return false;
			}
			String hint_prefix = itos(inner_type.builtin_type) + "/" + itos(variable->export_info.hint);
			variable->export_info.hint = PROPERTY_HINT_TYPE_STRING;
			variable->export_info.hint_string = hint_prefix + ":" + variable->export_info.hint_string;
			variable->export_info.type = Variant::ARRAY;
			return true;
		} else if (export_type.builtin_type == Variant::DICTIONARY) {
			variable->export_info.type = Variant::DICTIONARY;
			return true;
		} else if (export_type.builtin_type == Variant::PACKED_STRING_ARRAY) {
			String hint_prefix = itos(Variant::STRING) + "/" + itos(variable->export_info.hint);
			variable->export_info.hint = PROPERTY_HINT_TYPE_STRING;
			variable->export_info.hint_string = hint_prefix + ":" + variable->export_info.hint_string;
			variable->export_info.type = Variant::PACKED_STRING_ARRAY;
			return true;
		}
	}
	if (p_annotation->name == SNAME("@export")) {
		if (variable->datatype_specifier == nullptr && variable->initializer == nullptr) {