fix: update err-ignore test to accept new oasdiff output message

oasdiff now returns "No changes to report, but the specs are different"
when all breaking changes are suppressed via err-ignore, instead of
empty output (which the entrypoint mapped to "No breaking changes").

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: reuvenharrison

.github/workflows/test.yaml

@@ -322,7 +322,7 @@ jobs:
           ${{ steps.test_breaking_err_ignore.outputs.breaking }}
           $delimiter
           )
-          if [ "$output" != "No breaking changes" ]; then
-            echo "Expected 'No breaking changes' but got '$output'" >&2
+          if [ "$output" != "No changes to report, but the specs are different" ]; then
+            echo "Expected 'No changes to report, but the specs are different' but got '$output'" >&2
             exit 1
           fi