Disable deprecation warning for get_resource() (#805)

### Changelog
None

### Docs
None

### Description
See #804 for general description of the issue. Missed another API that
was deprecated. This should make the build pass now, verified by
enabling the ros2-testing repo in an ubuntu VM and building
successfully.

Fixes: FLE-165

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Silences deprecated API warnings in `message_definition_cache.cpp` for
compatibility across ROS2 distros.
> 
> - Wraps `ament_index_cpp::get_resource("rosidl_interfaces", ...)` with
`#pragma GCC diagnostic push/ignored("-Wdeprecated-declarations")`
(mirroring existing handling for `get_package_share_directory`)
> - No functional logic changes; build noise reduced
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
7aba2b6. 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

@@ -223,10 +223,15 @@ const MessageSpec& MessageDefinitionCache::load_message_spec(
 #pragma GCC diagnostic pop
 
   // Get the rosidl_interfaces index contents for this package
+  // 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"
   std::string index_contents;
   if (!ament_index_cpp::get_resource("rosidl_interfaces", package, index_contents)) {
     throw DefinitionNotFoundError(definition_identifier.package_resource_name);
   }
+#pragma GCC diagnostic pop
 
   // Find the first line that ends with the filename we're looking for
   const auto lines = split_string(index_contents);