self-hosted-runners: ensure post-deployment-script runs as administrator

During local testing, I forgot to run PowerShell as administrator and the installation of `pwsh` silently failed. Let's prevent the script from starting if we're not an admin.

Ref: https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_requires?view=powershell-7.4#-runasadministrator
Signed-off-by: Dennis Ameling <[email protected]>

Author: dennisameling

azure-self-hosted-runners/post-deployment-script.ps1

@@ -1,3 +1,5 @@
+#Requires -RunAsAdministrator
+
 param (
     # https://docs.github.com/en/actions/hosting-your-own-runners/adding-self-hosted-runners
     [Parameter(Mandatory = $true, HelpMessage = "GitHub Actions Runner registration token. Note that these tokens are only valid for one hour after creation, so we always expect the user to provide one.")]