Update appbar-theme-color.md (#12514)

Fix typo: hasve -> have in
`https://docs.flutter.dev/release/breaking-changes/appbar-theme-color`.

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I signed the CLA after I created this pull request.

Author: clemsciences

src/content/release/breaking-changes/appbar-theme-color.md

@@ -8,7 +8,7 @@ description: >-
 ## Summary
 
 The `color` parameter in `AppBarTheme` and `AppBarThemeData` constructors
-and their `copyWith` methods hasve been deprecated. Use `backgroundColor`
+and their `copyWith` methods have been deprecated. Use `backgroundColor`
 instead. This change affects how AppBar themes are configured and might
 cause deprecation warnings in existing code.