Fix CD smoke test by exercising Rust extension instead of for_file (#166)

The x86_64-linux smoke test in CD called CodeOwnership.for_file, which
requires config/code_ownership.yml in the CWD. This repo intentionally
does not ship that config (removed in e9f29ac), so the step failed with
"Can't open config file" on the first real dispatch after #157.

Replace the call with CodeOwnership.version, which exercises the
cross-compiled Rust native extension (loads the .so, calls into Rust)
without depending on a project config — the right check for a
platform-gem smoke test.

Prior smoke test (pre-#157) called a non-existent method with `|| true`,
so it silently no-op'd. #157 switched to a real method and dropped the
suppression, exposing the latent missing-config problem once CD next
ran on workflow_dispatch.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: perryqh

.github/workflows/cd.yml

@@ -72,8 +72,8 @@
             # Test that it works
             ruby -e "require 'code_ownership'; puts 'Version: ' + CodeOwnership::VERSION"
             
-            # Run a simple functionality test
-            ruby -e "require 'code_ownership'; puts CodeOwnership.for_file('lib/code_ownership.rb').inspect"
+            # Run a simple functionality test that exercises the Rust native extension
+            ruby -e "require 'code_ownership'; puts CodeOwnership.version"
             
             echo "✅ Successfully tested ${{ matrix.ruby-platform }} gem"