update banner with 3.11 (#7166)

Update site with Dart 3.11 Banner 

---

- [x] I’ve reviewed the contributor guide and applied the relevant
portions to this PR.
- [x] This PR doesn't contain automatically generated corrections or
text (Grammarly, LLMs, and similar).
- [x] This PR follows the [Google Developer Documentation Style
Guidelines](https://developers.google.com/style) — for example, it
doesn't use _i.e._ or _e.g._, and it avoids _I_ and _we_ (first person).
- [x] This PR uses [semantic line
breaks](https://github.com/dart-lang/site-shared/blob/main/doc/writing-for-dart-and-flutter-websites.md#semantic-line-breaks)
of 80 characters or fewer.

<details>
  <summary>Contribution guidelines:</summary><br>

- See our [contributor
guide](https://github.com/dart-lang/site-www/blob/main/CONTRIBUTING.md)
for general expectations for PRs.
- Larger or significant changes should be discussed in an issue before
creating a PR.
- Code changes should generally follow the [Dart style
guide](https://dart.dev/effective-dart) and use `dart format`.
- Updates to [code
excerpts](https://github.com/dart-lang/site-shared/blob/main/packages/excerpter)
indicated by `<?code-excerpt` need to be updated in their source `.dart`
file as well.
</details>

Author: conooi

src/data/banner.yml

@@ -1,7 +1,6 @@
 text: >-
-  Dart 3.10 is taking off with dot shorthands,
-  stable build hooks, nuanced deprecation annotations, and more!
+  Dart 3.11 is live!
 link:
   text: "Learn more"
-  url: "https://blog.dart.dev/announcing-dart-3-10-ea8b952b6088"
+  url: "https://blog.dart.dev/b6529be4203a"
   newTab: true