sdk: tighten ReadableSpan.attributes to non-Optional Mapping (#4569)#5183

WatchTree-19 wants to merge 2 commits intoopen-telemetry:mainopen-telemetry/opentelemetry-python:mainfrom

WatchTree-19:fix/readable-span-attributes-non-optionalWatchTree-19/opentelemetry-python:fix/readable-span-attributes-non-optionalCopy head branch name to clipboard