event resolver errors through to upbound-graphql when unable to get `involvedobject`

[jastang]

Hit this issue (slack thread) because the involvedobject (some pod) no longer existed, which would throw in xgql: https://github.com/upbound/xgql/blob/0a1d4aec8e2ad6c08ea831c603e1ea42ad0eec49/internal/graph/resolvers/event.go#L161

could we be more resilient?