Fix phpstan error in AiContextSubcontextToggleTrait
## Problem
On local, running ./lint.sh on 1.0.x, phpstan errors show up but the pipeline was green
```
Running phpstan (static analysis)...
165/165 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%
------ -------------------------------------------------------------------------------------------------------------
Line src/Service/AiContextSubcontextToggleTrait.php (in context of class Drupal\ai_context\Entity\AiContextItem)
------ -------------------------------------------------------------------------------------------------------------
31 Call to an undefined method Drupal\Core\TypedData\TypedDataInterface::get().
🪪 method.notFound
------ -------------------------------------------------------------------------------------------------------------
[ERROR] Found 1 error
✗ phpstan (static analysis) failed
```
## Solution
TBD
## Tasks
- Debug
- Fix code
- Review and test
issue