### 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 (path_state != PATH_STATE_START && path_state != PATH_STATE_SLASH) {
				push_error(R"("%" is only valid in the beginning of a node name (either after "$" or after "/"))");
				complete_extents(get_node);
				return nullptr;
			}
			get_node->full_path += "%";
			path_state = PATH_STATE_PERCENT;
		} else if (previous.type == GDScriptTokenizer::Token::SLASH) {
			if (path_state != PATH_STATE_START && path_state != PATH_STATE_NODE_NAME) {
				push_error(R"("/" is only valid at the beginning of the path or after a node name.)");
				complete_extents(get_node);
				return nullptr;
			}
			get_node->full_path += "/";
			path_state = PATH_STATE_SLASH;
		}
		make_completion_context(COMPLETION_GET_NODE, get_node, context_argument++);
		if (match(GDScriptTokenizer::Token::LITERAL)) {
			if (previous.literal.get_type() != Variant::STRING) {
				String previous_token;
				switch (path_state) {
					case PATH_STATE_START:
						previous_token = "$";
						break;
					case PATH_STATE_PERCENT:
						previous_token = "%";
						break;
					case PATH_STATE_SLASH:
						previous_token = "/";
						break;