### 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
temp_type.builtin_type = Variant::BOOL;
			GDScriptCodeGenerator::Address length_compat_addr = codegen.add_temporary(temp_type);
			codegen.generator->write_binary_operator(length_compat_addr, p_pattern->rest_used ? Variant::OP_GREATER_EQUAL : Variant::OP_EQUAL, value_length_addr, array_length_addr);
			codegen.generator->write_and_right_operand(length_compat_addr);
			
			codegen.generator->write_end_and(result_addr);
			
			codegen.generator->pop_temporary();
			codegen.generator->pop_temporary();
			
			GDScriptCodeGenerator::Address element_addr = codegen.add_temporary();
			GDScriptCodeGenerator::Address element_type_addr = codegen.add_temporary();
			
			for (int i = 0; i < p_pattern->array.size(); i++) {
				if (p_pattern->array[i]->pattern_type == GDScriptParser::PatternNode::PT_REST) {
					
					break;
				}
				
				codegen.generator->write_and_left_operand(result_addr);
				
				GDScriptCodeGenerator::Address index_addr = codegen.add_constant(i);
				
				codegen.generator->write_get(element_addr, index_addr, p_value_addr);
				
				Vector<GDScriptCodeGenerator::Address> typeof_args;
				typeof_args.push_back(element_addr);
				codegen.generator->write_call_utility(element_type_addr, "typeof", typeof_args);