Fix error serialization in resumable-upload.ts

[eagleeye]

Existing error handling has wrong error serialization with .toString(), that leads to [object Object] error messages. Example: Error: Retry limit exceeded - [object Object] at Upload.attemptDelayedRetry (/usr/src/app/node_modules/@google-cloud/storage/build/cjs/src/resumable-upload.js:818:26)

Better solution would be JSON.stringify the error

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