upgrade: update dependency flutter to v3.19.6 (#508)

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This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [flutter](https://flutter.dev)
([source](https://togithub.com/flutter/flutter)) | patch | `3.19.5` ->
`3.19.6` |

---

### Release Notes

<details>
<summary>flutter/flutter (flutter)</summary>

###
[`v3.19.6`](https://togithub.com/flutter/flutter/compare/3.19.5...3.19.6)

[Compare
Source](https://togithub.com/flutter/flutter/compare/3.19.5...3.19.6)

</details>

---

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.tool-versions

@@ -1,2 +1,2 @@
 dart 3.3.4
-flutter 3.19.5-stable
+flutter 3.19.6-stable