master: Update pkg/testutils/release/cockroach_releases.yaml

Update pkg/testutils/release/cockroach_releases.yaml with recent values.

Epic: None
Release note: None
Release justification: test-only updates

Author: cockroach-teamcity

pkg/testutils/release/cockroach_releases.yaml

@@ -50,4 +50,4 @@
 "26.2":
   predecessor: "26.1"
 "26.3":
-  predecessor: "26.1"
+  predecessor: "26.2"