Allow empty commits for the release (bytecodealliance#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]