ci: use `--github-workflow-markup` in the GitHub workflow

This makes the output easier to digest.

Note: since workflow output currently cannot contain any nested groups
(see https://github.com/actions/runner/issues/802 for details), we need
to remove the explicit grouping that would span the entirety of each
failed test script.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ci/lib.sh

@@ -177,7 +177,7 @@ then
 			test_name="${test_exit%.exit}"
 			test_name="${test_name##*/}"
 			printf "\\e[33m\\e[1m=== Failed test: ${test_name} ===\\e[m\\n"
-			group "Failed test: $test_name" cat "t/test-results/$test_name.out"
+			cat "t/test-results/$test_name.markup"
 
 			trash_dir="t/trash directory.$test_name"
 			cp "t/test-results/$test_name.out" t/failed-test-artifacts/
@@ -189,7 +189,7 @@ then
 	cache_dir="$HOME/none"
 
 	export GIT_PROVE_OPTS="--timer --jobs 10"
-	export GIT_TEST_OPTS="--verbose-log -x"
+	export GIT_TEST_OPTS="--verbose-log -x --github-workflow-markup"
 	MAKEFLAGS="$MAKEFLAGS --jobs=10"
 	test windows != "$CI_OS_NAME" ||
 	GIT_TEST_OPTS="--no-chain-lint --no-bin-wrappers $GIT_TEST_OPTS"