fix ci/release

by adding a stub commit there

ci/release

@@ -1,10 +1,11 @@
 #!/bin/bash
 set -xeuo pipefail
 
-parent_ref=$(git rev-parse HEAD)
 cd "$(git rev-parse --show-toplevel)"
+prev_ref=$(git rev-parse HEAD)
+git commit --allow-empty -m "this is a test commit"
 ./release --nosign v99.0
-cleanup() { git tag -d v99.0; git reset --hard "$parent_ref"; }
+cleanup() { git tag -d v99.0; git reset --hard "$prev_ref"; }
 trap cleanup EXIT
 
 want=" 1 file changed, 2 insertions(+), 2 deletions(-)"