Fix empty ADDED_SIZE env for restic>=0.14.0

[11mariom]

Since version 0.14.0 restic changed string for summary of backup, current version:

	b.P("%s to the repository: %-5s (%-5s stored)\n", verb,
		ui.FormatBytes(summary.ItemStats.DataSize+summary.ItemStats.TreeSize),
		ui.FormatBytes(summary.ItemStats.DataSizeInRepo+summary.ItemStats.TreeSizeInRepo))

https://github.com/restic/restic/blob/master/internal/ui/backup/text.go#L137-L139

old version (prior 0.13.1):

	b.P("%s to the repo: %-5s\n", verb, formatBytes(summary.ItemStats.DataSize+summary.ItemStats.TreeSize))

https://github.com/restic/restic/blob/v0.13.1/internal/ui/backup/text.go#L181

This MR is fixing issue of empty AUTORESTIC_ADDED_SIZE env variables for new restic versions and should work for old ones as well.

[vercel]

Someone is attempting to deploy a commit to a Personal Account owned by @cupcakearmy on Vercel.

@cupcakearmy first needs to authorize it.

[cupcakearmy]

Thanks!