### 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
push_multiline(true);
		advance();
		do {
			if (check(GDScriptTokenizer::Token::PARENTHESIS_CLOSE)) {
				
				break;
			}
			ParameterNode *parameter = parse_parameter();
			if (parameter == nullptr) {
				push_error("Expected signal parameter name.");
				break;
			}
			if (parameter->initializer != nullptr) {
				push_error(R"(Signal parameters cannot have a default value.)");
			}
			if (signal->parameters_indices.has(parameter->identifier->name)) {
				push_error(vformat(R"(Parameter with name "%s" was already declared for this signal.)", parameter->identifier->name));
			} else {
				signal->parameters_indices[parameter->identifier->name] = signal->parameters.size();
				signal->parameters.push_back(parameter);
			}
		} while (match(GDScriptTokenizer::Token::COMMA) && !is_at_end());
		pop_multiline();
		consume(GDScriptTokenizer::Token::PARENTHESIS_CLOSE, R"*(Expected closing ")" after signal parameters.)*");
	}
	complete_extents(signal);
	end_statement("signal declaration");
	return signal;
}
GDScriptParser::EnumNode *GDScriptParser::parse_enum(bool p_is_static) {