ci: avoid set-env construct in print-test-failures.sh

Imitating cac42e4 (ci: avoid using the deprecated `set-env`
construct, 2020-11-07), avoid deprecated ::set-env and use the
recommended alternative instead in print-test-failures.sh

Helped-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

ci/print-test-failures.sh

@@ -48,7 +48,7 @@ do
 			;;
 		github-actions)
 			mkdir -p failed-test-artifacts
-			echo "::set-env name=FAILED_TEST_ARTIFACTS::t/failed-test-artifacts"
+			echo "FAILED_TEST_ARTIFACTS=t/failed-test-artifacts" >>$GITHUB_ENV
 			cp "${TEST_EXIT%.exit}.out" failed-test-artifacts/
 			tar czf failed-test-artifacts/"$test_name".trash.tar.gz "$trash_dir"
 			continue