### 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
pop_multiline();
				complete_extents(call);
				return nullptr;
			}
			if (current_function->identifier) {
				call->function_name = current_function->identifier->name;
			} else {
				call->function_name = SNAME("<anonymous>");
			}
		} else {
			consume(GDScriptTokenizer::Token::PERIOD, R"(Expected "." or "(" after "super".)");
			make_completion_context(COMPLETION_SUPER_METHOD, call, true);
			if (!consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected function name after ".".)")) {
				pop_multiline();
				complete_extents(call);
				return nullptr;
			}
			IdentifierNode *identifier = parse_identifier();
			call->callee = identifier;
			call->function_name = identifier->name;
			consume(GDScriptTokenizer::Token::PARENTHESIS_OPEN, R"(Expected "(" after function name.)");
		}
	} else {
		call->callee = p_previous_operand;
		if (call->callee == nullptr) {
			push_error(R"*(Cannot call on an expression. Use ".call()" if it's a Callable.)*");
		} else if (call->callee->type == Node::IDENTIFIER) {
			call->function_name = static_cast<IdentifierNode *>(call->callee)->name;
			make_completion_context(COMPLETION_METHOD, call->callee);
		} else if (call->callee->type == Node::SUBSCRIPT) {