Patch Enumerator#next to get better stack traces

What does this MR do and why?

Enumerator#next has poor stack traces due to https://bugs.ruby-lang.org/issues/16829. Append the caller's stack trace to the raised exception.

Found while working on #342703 (closed). Gitlab::GitalyClient::Call#instrument_stream calls Enumerator#next. which means that exceptions thrown while reading from a GRPC stream (in this case a GRPC::DeadlineExceeded) contain only the backtrace information from GRPC itself, since that's all that's running in the Fiber created by #next

Example stacktrace: !88882 (comment 994128140)

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