### 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
switch (p_variable->property) {
		case VariableNode::PROP_INLINE: {
			FunctionNode *function = alloc_node<FunctionNode>();
			consume(GDScriptTokenizer::Token::COLON, R"(Expected ":" after "get".)");
			IdentifierNode *identifier = alloc_node<IdentifierNode>();
			complete_extents(identifier);
			identifier->name = "@" + p_variable->identifier->name + "_getter";
			function->identifier = identifier;
			function->is_static = p_variable->is_static;
			FunctionNode *previous_function = current_function;
			current_function = function;
			SuiteNode *body = alloc_node<SuiteNode>();
			function->body = parse_suite("getter declaration", body);
			p_variable->getter = function;
			current_function = previous_function;
			complete_extents(function);
			break;
		}
		case VariableNode::PROP_SETGET:
			consume(GDScriptTokenizer::Token::EQUAL, R"(Expected "=" after "get")");
			make_completion_context(COMPLETION_PROPERTY_METHOD, p_variable);
			if (consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected getter function name after "=".)")) {
				p_variable->getter_pointer = parse_identifier();
			}
			break;
		case VariableNode::PROP_NONE:
			break; 
	}
}
GDScriptParser::ConstantNode *GDScriptParser::parse_constant(bool p_is_static) {