Add type expectation to warning message for payload metrics value parsing. I found it hard to debug with similar messages for 3 different conditions.
Add type expectation to warning message for payload metrics value parsing. I found it hard to debug with similar messages for 3 different conditions.

PiperOrigin-RevId: 220816776

google/cloudprober,cloudprober/cloudprober,cloudprober/cloudprober,cloudprober/cloudprober,google/cloudprober