ci: add missing "outputs CARGO_FEATURES_OPTION"

Author: cakebaker

.github/workflows/ci.yml

@@ -104,6 +104,7 @@ jobs:
         # target-specific options
         # * CARGO_FEATURES_OPTION
         CARGO_FEATURES_OPTION='--all -- --check' ;  ## default to '--all-features' for code coverage
+        outputs CARGO_FEATURES_OPTION
         # * CODECOV_FLAGS
         CODECOV_FLAGS=$( echo "${{ matrix.job.os }}" | sed 's/[^[:alnum:]]/_/g' )
         outputs CODECOV_FLAGS