fix(ng-dev/release): allow empty commits when publishing snapshots

When publishing snapshots, it's possible that a package is built but
contains no functional changes (e.g. only version placeholder updates
which are ignored by the diff).

Previously, the git commit step would fail in these cases because the
working tree was clean. This change adds the --allow-empty flag to
ensure the commit succeeds regardless of changes.

Author: alan-agius4

ng-dev/release/snapshot-publish/snapshots.ts

@@ -161,9 +161,11 @@ export class SnapshotPublisher {
             ['diff-index', '--quiet', '-I', '0\\.0\\.0-[a-f0-9]+', 'HEAD', '--'],
             {cwd: tmpRepoDir},
           ).status === 1;
+
         this.git.run(
           [
             'commit',
+            '--allow-empty',
             '--author',
             this.commitAuthor,
             '-m',