Bump windows/nanoserver from 1903 to 1909 in /release/preview/nanoserver1809/dependabot#334

dependabot-preview[bot] wants to merge 1 commit intomasterPowerShell/PowerShell-Docker:masterfrom

dependabot/docker/release/preview/nanoserver1809/dependabot/windows/nanoserver-1909PowerShell/PowerShell-Docker:dependabot/docker/release/preview/nanoserver1809/dependabot/windows/nanoserver-1909Copy head branch name to clipboard