### 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
p_script->constants.insert(name, enum_value.value);
			} break;
			case GDScriptParser::ClassNode::Member::SIGNAL: {
				const GDScriptParser::SignalNode *signal = member.signal;
				StringName name = signal->identifier->name;
				Vector<StringName> parameters_names;
				parameters_names.resize(signal->parameters.size());
				for (int j = 0; j < signal->parameters.size(); j++) {
					parameters_names.write[j] = signal->parameters[j]->identifier->name;
				}
				p_script->_signals[name] = parameters_names;
			} break;
			case GDScriptParser::ClassNode::Member::ENUM: {
				const GDScriptParser::EnumNode *enum_n = member.m_enum;
				StringName name = enum_n->identifier->name;
				p_script->constants.insert(name, enum_n->dictionary);
			} break;
			case GDScriptParser::ClassNode::Member::GROUP: {
				const GDScriptParser::AnnotationNode *annotation = member.annotation;
				StringName name = annotation->export_info.name;
				
				GDScript::MemberInfo minfo;
				minfo.index = p_script->member_indices.size();
				PropertyInfo prop_info;
				prop_info.name = name;
				prop_info.usage = annotation->export_info.usage;
				prop_info.hint_string = annotation->export_info.hint_string;
				p_script->member_info[name] = prop_info;
				p_script->member_indices[name] = minfo;
				p_script->members.insert(name);