Ignore import changes in public API check (#6855)

## Summary
Ignores regular import lines when diffing generated public Swift
interfaces. For example, #6845 reports the removal of import
CoreGraphics as a public API change even though it doesn’t change the
API exposed to SDK users.

## Motivation
#6845

## Testing
- Ruby syntax check
- Verified regular imports are filtered while exported imports remain in
the diff

## Changelog
N/A

Co-authored-by: codex <noreply@openai.com>

Author: porter-stripe

ci_scripts/api_diff/diff_public_interface.rb

@@ -82,7 +82,9 @@ def write_output(path, content)
 
   master_public_interface_path = "#{framework_name}-master.xcframework/#{simulator_slice}/#{public_interface_dir}/arm64-apple-ios-simulator.swiftinterface"
   branch_public_interface_path = "#{framework_name}-new.xcframework/#{simulator_slice}/#{public_interface_dir}/arm64-apple-ios-simulator.swiftinterface"
-  public_diff_lines = sorted_diff_lines(master_public_interface_path, branch_public_interface_path)
+  public_diff_lines = sorted_diff_lines(master_public_interface_path, branch_public_interface_path).reject do |line|
+    line.match?(/^[+-]import\s/)
+  end
 
   master_private_interface_path = "#{framework_name}-master.xcframework/#{simulator_slice}/#{public_interface_dir}/arm64-apple-ios-simulator.private.swiftinterface"
   branch_private_interface_path = "#{framework_name}-new.xcframework/#{simulator_slice}/#{public_interface_dir}/arm64-apple-ios-simulator.private.swiftinterface"