chore(ci): new pre-release 3.9.1a0 (#6354)

Co-authored-by: Powertools for AWS Lambda (Python) bot <151832416+aws-powertools-bot@users.noreply.github.com>

Author: github-actions[bot]

aws_lambda_powertools/shared/version.py

@@ -1,3 +1,3 @@
 """Exposes version constant to avoid circular dependencies."""
 
-VERSION = "3.9.0"
+VERSION = "3.9.1a0"