### 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
Vector<GDScriptCodeGenerator::Address> args;
							args.push_back(assigned);
							GDScriptCodeGenerator::Address call_base = is_static ? GDScriptCodeGenerator::Address(GDScriptCodeGenerator::Address::CLASS) : GDScriptCodeGenerator::Address(GDScriptCodeGenerator::Address::SELF);
							gen->write_call(GDScriptCodeGenerator::Address(), call_base, member_property_setter_function, args);
						} else if (is_static) {
							GDScriptCodeGenerator::Address temp = codegen.add_temporary(static_var_data_type);
							gen->write_assign(temp, assigned);
							gen->write_set_static_variable(temp, static_var_class, static_var_index);
							gen->pop_temporary();
						} else {
							gen->write_assign(target_member_property, assigned);
						}
						if (!known_type) {
							gen->write_end_jump_if_shared();
						}
					}
				}
				if (assigned.mode == GDScriptCodeGenerator::Address::TEMPORARY) {
					gen->pop_temporary();
				}
			} else if (assignment->assignee->type == GDScriptParser::Node::IDENTIFIER && _is_class_member_property(codegen, static_cast<GDScriptParser::IdentifierNode *>(assignment->assignee)->name)) {
				
				GDScriptCodeGenerator::Address assigned_value = _parse_expression(codegen, r_error, assignment->assigned_value);
				if (r_error) {
					return GDScriptCodeGenerator::Address();
				}
				GDScriptCodeGenerator::Address to_assign = assigned_value;
				bool has_operation = assignment->operation != GDScriptParser::AssignmentNode::OP_NONE;
				StringName name = static_cast<GDScriptParser::IdentifierNode *>(assignment->assignee)->name;
				if (has_operation) {