Prior to this commit, the `DefaultExecutionRequestObservationConvention`
would only produce "INTERNAL_ERROR" outcomes if the response is null or
if an unresolved exception remains.
The `ExceptionResolversExceptionHandler` will catch all unresolved
exceptions and add them to the errors map with the
`ErorType.INTERNAL_ERROR` error type. This means that the
"INTERNAL_ERROR" outcome is never used.
This commit ensures that this outcome is also used if at least one
resolved error is of `ErorType.INTERNAL_ERROR`.
Fixes gh-1058
d7ed85045b