Merge pull request #146243 from cockroachdb/blathers/backport-release-25.2-146219

release-25.2: roachtest: deflake declarative_schema_changer/job-compatibility-mixed-version

Author: fqazi

pkg/cmd/roachtest/tests/mixed_version_job_compatibility_in_declarative_schema_changer.go

@@ -55,6 +55,11 @@ func setShortJobIntervalsStep(
 func setShortGCTTLInSystemZoneConfig(
 	ctx context.Context, l *logger.Logger, r *rand.Rand, h *mixedversion.Helper,
 ) error {
+	// Ensure the system database has a longer TTL interval, which is needed to avoid
+	// flakes on system database queries for upgrades.
+	if err := h.Exec(r, "ALTER DATABASE system CONFIGURE ZONE USING gc.ttlseconds=60;"); err != nil {
+		return err
+	}
 	return h.Exec(r, "ALTER RANGE default CONFIGURE ZONE USING gc.ttlseconds = 1;")
 }