github: pass GITHUB_ACTIONS to test scripts (canonical#356)

Fixes bug I introduced when trying to avoid text walls in `cleanup()` on
failure. I didn't think of `sudo` stripping the environment.

.github/workflows/tests.yml

@@ -283,7 +283,7 @@ jobs:
             src_track="$(echo "${dst_track}" | cut -d/ -f1)/stable"
             EXTRA_ARGS="${EXTRA_ARGS:-3} ${src_track} ${{ matrix.track }}"
           fi
-          sudo --preserve-env=GITHUB_STEP_SUMMARY,TEST_IMG ./bin/local-run "tests/${TEST_SCRIPT}" ${{ matrix.track }} ${EXTRA_ARGS:-}
+          sudo --preserve-env=GITHUB_ACTIONS,GITHUB_STEP_SUMMARY,TEST_IMG ./bin/local-run "tests/${TEST_SCRIPT}" ${{ matrix.track }} ${EXTRA_ARGS:-}
 
       # always update cache as we have our own logic of
       # cache invalidation and updates in addition to a date check