### 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
*/
					int open_bracket_pos = begin_scan, close_bracket_pos = 0;
					while (open_bracket_pos < stripped_line.length() && (stripped_line[open_bracket_pos] == ' ' || stripped_line[open_bracket_pos] == '\t')) {
						open_bracket_pos++;
					}
					if (open_bracket_pos == stripped_line.length() || stripped_line[open_bracket_pos++] != '(') {
						continue; 
					}
					close_bracket_pos = open_bracket_pos;
					while (close_bracket_pos < stripped_line.length() && stripped_line[close_bracket_pos] != ')') {
						close_bracket_pos++;
					}
					if (close_bracket_pos == stripped_line.length()) {
						continue; 
					}
					int colon_pos = close_bracket_pos + 1;
					while (colon_pos < stripped_line.length() && (stripped_line[colon_pos] == ' ' || stripped_line[colon_pos] == '\t')) {
						colon_pos++;
					}
					if (colon_pos == stripped_line.length() || stripped_line[colon_pos++] != ':') {
						continue; 
					}
					title = stripped_line.substr(open_bracket_pos, close_bracket_pos - open_bracket_pos).strip_edges();
					link = stripped_line.substr(colon_pos).strip_edges();
				}
				mode = TUTORIALS;
			} else if (mode == TUTORIALS) { 
				mode = DONE;
			}
		}