### 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
if (is_awaited) {
								gen->write_call_async(result, self, call->function_name, arguments);
							} else {
								gen->write_call(result, self, call->function_name, arguments);
							}
						} else {
							if (is_awaited) {
								gen->write_call_self_async(result, call->function_name, arguments);
							} else {
								gen->write_call_self(result, call->function_name, arguments);
							}
						}
					} else if (callee->type == GDScriptParser::Node::SUBSCRIPT) {
						const GDScriptParser::SubscriptNode *subscript = static_cast<const GDScriptParser::SubscriptNode *>(call->callee);
						if (subscript->is_attribute) {
							
							if (!call->is_super && subscript->base->type == GDScriptParser::Node::IDENTIFIER && GDScriptParser::get_builtin_type(static_cast<GDScriptParser::IdentifierNode *>(subscript->base)->name) < Variant::VARIANT_MAX) {
								gen->write_call_builtin_type_static(result, GDScriptParser::get_builtin_type(static_cast<GDScriptParser::IdentifierNode *>(subscript->base)->name), subscript->attribute->name, arguments);
							} else if (!call->is_super && subscript->base->type == GDScriptParser::Node::IDENTIFIER && call->function_name != SNAME("new") &&
									ClassDB::class_exists(static_cast<GDScriptParser::IdentifierNode *>(subscript->base)->name) && !Engine::get_singleton()->has_singleton(static_cast<GDScriptParser::IdentifierNode *>(subscript->base)->name)) {
								
								gen->write_call_native_static(result, static_cast<GDScriptParser::IdentifierNode *>(subscript->base)->name, subscript->attribute->name, arguments);
							} else {
								GDScriptCodeGenerator::Address base = _parse_expression(codegen, r_error, subscript->base);
								if (r_error) {
									return GDScriptCodeGenerator::Address();
								}
								if (is_awaited) {
									gen->write_call_async(result, base, call->function_name, arguments);
								} else if (base.type.has_type && base.type.kind != GDScriptDataType::BUILTIN) {