Bump pigeon from 20.0.2 to 21.0.0 in /add_to_app/books/flutter_module_books (#2355)

Bumps [pigeon](https://github.com/flutter/packages/tree/main/packages)
from 20.0.2 to 21.0.0.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/flutter/packages/commit/3379e51a042af5efe5c5e1e69e0f3ce5d979351f"><code>3379e51</code></a>
[pigeon] Fix C++ enum naming (<a
href="https://github.com/flutter/packages/tree/main/packages/issues/7094">#7094</a>)</li>
<li><a
href="https://github.com/flutter/packages/commit/33caf1d3d5b1e38bcbf326ffb14d67a966abaff6"><code>33caf1d</code></a>
[ios]Fix compile error when conforming UIApplication to Launcher due to
MainA...</li>
<li><a
href="https://github.com/flutter/packages/commit/21e3340a952f31fda4c8c610643c2026f52bf43a"><code>21e3340</code></a>
[go_router] Makes GoRouterState lookup more robust. (<a
href="https://github.com/flutter/packages/tree/main/packages/issues/6920">#6920</a>)</li>
<li><a
href="https://github.com/flutter/packages/commit/da04812172c75d9225701ba6d3758c4de517288d"><code>da04812</code></a>
[ci][web] Run tests in canvaskit mode. (<a
href="https://github.com/flutter/packages/tree/main/packages/issues/6879">#6879</a>)</li>
<li><a
href="https://github.com/flutter/packages/commit/0ae6dda5d133bebe3b7eb511fea3ecb2c69321ec"><code>0ae6dda</code></a>
[image_picker]: Bump androidx.core:core from 1.10.1 to 1.13.1 in
/packages/im...</li>
<li><a
href="https://github.com/flutter/packages/commit/ea35fc6fb86a76675030581d745221d32f80226b"><code>ea35fc6</code></a>
[camera_avfoundation] Adds Swift Package Manager compatibility (<a
href="https://github.com/flutter/packages/tree/main/packages/issues/7080">#7080</a>)</li>
<li><a
href="https://github.com/flutter/packages/commit/57d42e447c6a6596c3eab43a226a5879f8029d40"><code>57d42e4</code></a>
[webview_flutter_wkwebview] Adds Swift Package Manager compatibility (<a
href="https://github.com/flutter/packages/tree/main/packages/issues/7091">#7091</a>)</li>
<li><a
href="https://github.com/flutter/packages/commit/c47614c6d984fb42028ebb24fa0a64acfd15d253"><code>c47614c</code></a>
[webview_flutter_web] Migrate to package:web. (<a
href="https://github.com/flutter/packages/tree/main/packages/issues/6792">#6792</a>)</li>
<li><a
href="https://github.com/flutter/packages/commit/17188b758b448a16c7016552255cbf456a1bb170"><code>17188b7</code></a>
[camera] Clean up <code>maxDuration</code> code (<a
href="https://github.com/flutter/packages/tree/main/packages/issues/7039">#7039</a>)</li>
<li><a
href="https://github.com/flutter/packages/commit/007ec6676fe7d1530fd4c2d1b6e5696cedb815b7"><code>007ec66</code></a>
Update espresso dependencies (<a
href="https://github.com/flutter/packages/tree/main/packages/issues/7048">#7048</a>)</li>
<li>Additional commits viewable in <a
href="https://github.com/flutter/packages/commits/pigeon-v21.0.0/packages">compare
view</a></li>
</ul>
</details>
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add_to_app/books/flutter_module_books/pubspec.yaml

@@ -15,7 +15,7 @@ dependencies:
 dev_dependencies:
   analysis_defaults:
     path: ../../../analysis_defaults
-  pigeon: ">=11.0.0 <21.0.0"
+  pigeon: ">=11.0.0 <22.0.0"
   flutter_test:
     sdk: flutter