release: released CockroachDB version 25.3.0-alpha.1. Next version: 25.3.0-alpha.2

Release note: None
Epic: None
Release justification: non-production (release infra) change.

Author: cockroach-teamcity

pkg/build/version.txt

@@ -1 +1 @@
-v25.3.0-alpha.1
+v25.3.0-alpha.2