Update to Velero 1.9.0 breaks restic with custom CA

[timbuchwaldt]

What steps did you take and what happened:
After updating to Velero 1.9.0 via the Helm chart we saw all Restic backups fail. We use a custom CA Cert for the internal S3 compliant backup stoarge.
The following error is reported:

stderr=unable to read root certificate: open /tmp/cacert-default3164165714: no such file or directory
github.com/restic/restic/internal/backend.Transport
/restic/internal/backend/http_transport.go:110
main.open
    /restic/cmd/restic/global.go:687
main.OpenRepository
    /restic/cmd/restic/global.go:421
main.runBackup
    /restic/cmd/restic/cmd_backup.go:524
main.glob..func2
    /restic/cmd/restic/cmd_backup.go:61
github.com/spf13/cobra.(*Command).execute
    /home/build/go/pkg/mod/github.com/spf13/[email protected]/command.go:856
github.com/spf13/cobra.(*Command).ExecuteC
    /home/build/go/pkg/mod/github.com/spf13/[email protected]/command.go:974
github.com/spf13/cobra.(*Command).Execute
    /home/build/go/pkg/mod/github.com/spf13/[email protected]/command.go:902
main.main
    /restic/cmd/restic/main.go:98
runtime.main
    /usr/local/go/src/runtime/proc.go:250
runtime.goexit
    /usr/local/go/src/runtime/asm_amd64.s:1571
: exit status 1

A rollback to the 1.8.1 release works perfectly.

The config looks something like this:

          configuration:
              provider: aws
              backupStorageLocation:
                bucket: k8s-backups
                caCert: <base64 crt>
                config:
                  region: us-east-1
                  s3ForcePathStyle: "true"
                  s3Url: https://my-funny-s3.local
              volumeSnapshotLocation:
                config:
                  region: us-east-1
              defaultVolumesToRestic: true

What did you expect to happen:
Succesful backups with our custom CA.

Environment:

Client:
	Version: v1.9.0
	Git commit: 6021f148c4d7721285e815a3e1af761262bff029
Server:
	Version: v1.8.1

• Velero features (use velero client config get features): NOT SET
• Kubernetes version (use kubectl version): 1.23.7/1.22

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