Update GitHub skill to use gh cli to access private repo content

[ptr727]

$ curl -fsSL "https://raw.githubusercontent.com/ptr727/HomeAutomation-Config/cloudinit-vm-provisioning/CloudInit/install-powershell.sh"
curl: (22) The requested URL returned error: 404

$ gh api repos/ptr727/HomeAutomation-Config/contents/CloudInit/install-powershell.sh?ref=cloudinit-vm-provisioning --jq '.content' 2>&1 | base64 -d
base64: invalid input

$ gh api "repos/ptr727/HomeAutomation-Config/contents/CloudInit/install-powershell.sh?ref=cloudinit-vm-provisioning" --jq '.content' > /tmp/opencode/install-powershell.b64 && base64 -d /tmp/opencode/install-powershell.b64
gh: No commit found for the ref cloudinit-vm-provisioning (HTTP 404)

$ gh api "repos/ptr727/HomeAutomation-Config/contents/CloudInit/install-powershell.sh?ref=420ef7528bf69401f19e3c80a0c6c810c6b04c7e" --jq '.content' | base64 -d
#!/bin/bash
#
# Installs, upgrades, or removes PowerShell (pwsh) from the portable Linux tar.gz build, under
# /opt/microsoft/powershell/7 with a /usr/local/bin/pwsh symlink -- not from Microsoft's apt repo,
# which currently only publishes as far as Debian 12 "bookworm" and this host is Debian 13
# "trixie". The tar.gz build bundles its own .NET runtime and ICU, so it installs the same way
# regardless of host distro/version, the same reasoning install-tools.sh already applies to jq
# and uv.
#
# pwsh is this directory's prerequisite for Fido.ps1 (Windows 11 ISO URL lookup) -- see