### 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
type->type_chain.push_back(type_element);
	if (match(GDScriptTokenizer::Token::BRACKET_OPEN)) {
		
		type->container_type = parse_type(false); 
		if (type->container_type == nullptr) {
			push_error(R"(Expected type for collection after "[".)");
			complete_extents(type);
			type = nullptr;
		} else if (type->container_type->container_type != nullptr) {
			push_error("Nested typed collections are not supported.");
		}
		consume(GDScriptTokenizer::Token::BRACKET_CLOSE, R"(Expected closing "]" after collection type.)");
		if (type != nullptr) {
			complete_extents(type);
		}
		return type;
	}
	int chain_index = 1;
	while (match(GDScriptTokenizer::Token::PERIOD)) {
		make_completion_context(COMPLETION_TYPE_ATTRIBUTE, type, chain_index++);
		if (consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected inner type name after ".".)")) {
			type_element = parse_identifier();
			type->type_chain.push_back(type_element);
		}
	}
	complete_extents(type);
	return type;
}
#ifdef TOOLS_ENABLED
enum DocLineState {