### 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
return parse_variable(p_is_static, true);
}
GDScriptParser::VariableNode *GDScriptParser::parse_variable(bool p_is_static, bool p_allow_property) {
	VariableNode *variable = alloc_node<VariableNode>();
	if (!consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected variable name after "var".)")) {
		complete_extents(variable);
		return nullptr;
	}
	variable->identifier = parse_identifier();
	variable->export_info.name = variable->identifier->name;
	variable->is_static = p_is_static;
	if (match(GDScriptTokenizer::Token::COLON)) {
		if (check(GDScriptTokenizer::Token::NEWLINE)) {
			if (p_allow_property) {
				advance();
				return parse_property(variable, true);
			} else {
				push_error(R"(Expected type after ":")");
				complete_extents(variable);
				return nullptr;
			}
		} else if (check((GDScriptTokenizer::Token::EQUAL))) {
			
			variable->infer_datatype = true;
		} else {
			if (p_allow_property) {
				make_completion_context(COMPLETION_PROPERTY_DECLARATION_OR_TYPE, variable);
				if (check(GDScriptTokenizer::Token::IDENTIFIER)) {