Add PRR beta approver for KEP-5440

Fixes the verification checks by adding the required beta approver
to the Production Readiness Review file. The PRR file needs an approver
for each milestone stage (alpha, beta, stable).

Author: kannon92

keps/prod-readiness/sig-apps/5440.yaml

@@ -1,4 +1,6 @@
 kep-number: 5440
 alpha:
   approver: "@jpbetz"
+beta:
+  approver: "@jpbetz"