release: released CockroachDB version 25.2.0-alpha.3. Next version: 25.2.0-alpha.4

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

Author: cockroach-teamcity

pkg/build/version.txt

@@ -1 +1 @@
-v25.2.0-alpha.3
+v25.2.0-alpha.4