### 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
String script_path;
	bool for_completion = false;
	bool panic_mode = false;
	bool can_break = false;
	bool can_continue = false;
	List<bool> multiline_stack;
	ClassNode *head = nullptr;
	Node *list = nullptr;
	List<ParserError> errors;
#ifdef DEBUG_ENABLED
	bool is_ignoring_warnings = false;
	List<GDScriptWarning> warnings;
	HashSet<GDScriptWarning::Code> ignored_warnings;
	HashSet<int> unsafe_lines;
#endif
	GDScriptTokenizer tokenizer;
	GDScriptTokenizer::Token previous;
	GDScriptTokenizer::Token current;
	ClassNode *current_class = nullptr;
	FunctionNode *current_function = nullptr;
	SuiteNode *current_suite = nullptr;
	CompletionContext completion_context;
	CompletionCall completion_call;
	List<CompletionCall> completion_call_stack;
	bool passed_cursor = false;
	bool in_lambda = false;
	bool lambda_ended = false; 
	typedef bool (GDScriptParser::*AnnotationAction)(const AnnotationNode *p_annotation, Node *p_target);
	struct AnnotationInfo {
		enum TargetKind {