[PHP-NOTES] note 130686 added to function.is-writable

I've encountered an unexpected issue: even though the directory allows writing files, it keeps returning false.

```
$a = 'C:/Users/*/OneDrive/work/www/';
$b = "{$a}admin/";
var_dump($a);
var_dump(is_writable($a));
var_dump($b);
var_dump(is_dir($b));
var_dump(is_writable($b));
var_dump(file_put_contents($b.'test.txt','hello'));
```

- string 'C:/Users/*/OneDrive/work/www/' (length=33)
- boolean true
- string 'C:/Users/*/OneDrive/work/www/admin/' (length=39)
- boolean true
- boolean false
- int 5
----
Server IP: 206.189.2.9
Probable Submitter: 222.213.202.49
----
Manual Page -- https://php.net/manual/en/function.is-writable.php
Edit        -- https://main.php.net/note/edit/130686
Del: integrated  -- https://main.php.net/note/delete/130686/integrated
Del: useless     -- https://main.php.net/note/delete/130686/useless
Del: bad code    -- https://main.php.net/note/delete/130686/bad+code
Del: spam        -- https://main.php.net/note/delete/130686/spam
Del: non-english -- https://main.php.net/note/delete/130686/non-english
Del: in docs     -- https://main.php.net/note/delete/130686/in+docs
Del: other reasons-- https://main.php.net/note/delete/130686
Reject      -- https://main.php.net/note/reject/130686
Search      -- https://main.php.net/manage/user-notes.php