Allow empty commits for the release (#4927)

The release process failed last night due to me filling out the dates in
the release notes early (rather than leaving "Unreleased") which mean
there were no changes for each commit. Switch to passing `--allow-empty`
when making a commit to prevent this.

.github/workflows/release-process.yml

@@ -117,7 +117,7 @@ jobs:
  rustc ci/update-release-date.rs -o /tmp/update-release-date
  /tmp/update-release-date $(date +'%Y-%m-%d')
 
- git commit -a -F-<<EOF
+ git commit --allow-empty -a -F-<<EOF
  Update release date of Wasmtime $cur
  EOF
  git push origin HEAD:ci/release-date-for-$cur
@@ -152,7 +152,7 @@ jobs:
  # released
  git reset --hard origin/release-$cur
  sed -i "s/^Unreleased/Released $(date +'%Y-%m-%d')/" RELEASES.md
- git commit -a -F-<<EOF
+ git commit --allow-empty -a -F-<<EOF
  Release Wasmtime $cur
 
  [automatically-tag-and-release-this-commit]