### 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 GDScriptCodeGenerator::Address();
			}
			gen->write_ternary_true_expr(true_expr);
			if (true_expr.mode == GDScriptCodeGenerator::Address::TEMPORARY) {
				gen->pop_temporary();
			}
			GDScriptCodeGenerator::Address false_expr = _parse_expression(codegen, r_error, ternary->false_expr);
			if (r_error) {
				return GDScriptCodeGenerator::Address();
			}
			gen->write_ternary_false_expr(false_expr);
			if (false_expr.mode == GDScriptCodeGenerator::Address::TEMPORARY) {
				gen->pop_temporary();
			}
			gen->write_end_ternary();
			return result;
		} break;
		case GDScriptParser::Node::TYPE_TEST: {
			const GDScriptParser::TypeTestNode *type_test = static_cast<const GDScriptParser::TypeTestNode *>(p_expression);
			GDScriptCodeGenerator::Address result = codegen.add_temporary(_gdtype_from_datatype(type_test->get_datatype(), codegen.script));
			GDScriptCodeGenerator::Address operand = _parse_expression(codegen, r_error, type_test->operand);
			GDScriptDataType test_type = _gdtype_from_datatype(type_test->test_datatype, codegen.script);
			if (r_error) {
				return GDScriptCodeGenerator::Address();
			}
			if (test_type.has_type) {
				gen->write_type_test(result, operand, test_type);
			} else {
				gen->write_assign_true(result);
			}