Suppress deprecation warning for ament_index API (#804)

### Changelog
None

### Docs
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### Description
Temporarily suppress deprecation warnings for
`get_package_share_directory`, which will cause ROS2 buildfarm builds to
pass for Foxglove Bridge. These suppressions will be reverted in #803
once ament/ament_index#105 has merged and ROS packages have synced.

Fixes: FLE-165

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Temporarily mutes deprecation warnings to unblock ROS2 builds.
> 
> - Wraps `ament_index_cpp::get_package_share_directory` call in
`message_definition_cache.cpp` with GCC pragmas to ignore
`-Wdeprecated-declarations`
> - Adds TODO noting removal after `ament_index_cpp` update (FLE-167)
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
14325f4. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: ericmlujan

ros/src/foxglove_bridge/src/message_definition_cache.cpp

@@ -215,7 +215,12 @@ const MessageSpec& MessageDefinitionCache::load_message_spec(
   }
 
   // Get the package share directory, or throw a PackageNotFoundError
+  // TODO: FLE-167: Remove warning once ament_index_cpp is updated and synced across all current
+  // ROS2 distributions.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
   const std::string share_dir = ament_index_cpp::get_package_share_directory(package);
+#pragma GCC diagnostic pop
 
   // Get the rosidl_interfaces index contents for this package
   std::string index_contents;