vagrant: Unbreak replacing symlinks on macOS
vagrant: Unbreak replacing symlinks on macOS

On a local installation on macOS, "cp -a" creates a write-protected
directory, which can't be renamed.  Do a "chmod +w" to unbreak.

Fixes #77671.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs