fix(ng-dev/release): skip commit in snapshot repository if no changes are detected

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

Previously, we would still attempt to run `git commit`, which would fail if no  changes were staged. This change wraps the commit call in a check for changes,  avoiding empty commits or errors.

Author: alan-agius4

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

@@ -161,16 +161,19 @@ export class SnapshotPublisher {
             ['diff-index', '--quiet', '-I', '0\\.0\\.0-[a-f0-9]+', 'HEAD', '--'],
             {cwd: tmpRepoDir},
           ).status === 1;
-        this.git.run(
-          [
-            'commit',
-            '--author',
-            this.commitAuthor,
-            '-m',
-            `"${this.snapshotCommitMessage.replace(/"/g, '\\"')}"`,
-          ],
-          {cwd: tmpRepoDir},
-        );
+
+        if (containsChanges) {
+          this.git.run(
+            [
+              'commit',
+              '--author',
+              this.commitAuthor,
+              '-m',
+              `"${this.snapshotCommitMessage.replace(/"/g, '\\"')}"`,
+            ],
+            {cwd: tmpRepoDir},
+          );
+        }
 
         return {
           url,