fix: correct typings for SourceContext (#626)
fix: correct typings for SourceContext (#626)

Ref: https://cloud.google.com/debugger/api/reference/rest/v2/Debuggee#SourceContext
DominicKramer/cloud-debug-nodejs,DominicKramer/cloud-debug-nodejs,googleapis/cloud-debug-nodejs,DominicKramer/cloud-debug-nodejs,googleapis/cloud-debug-nodejs,googleapis/cloud-debug-nodejs