[Windows] cli: fix incorrect filepath separator causing upgrades to fail

[daniel-weisse]

Proposed change(s)

• Fix incorrect usage of path.Dir() (instead of filepath.Dir()) that breaks directory backups for the Constellation CLI on Windows.
  • This effectively made the CLI unable to run constellation upgrade apply on Windows systems
  • Detected because we run the Terraform state backup as part of constellation apply, which is called during the initialization process

Additional info

• e2e test Windows

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