Bump windows/servercore from 1903 to 1909 in /release/preview/windowsservercore/dependabot#11

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dependabot/docker/release/preview/windowsservercore/dependabot/windows/servercore-1909TravisEz13/PowerShell-Docker:dependabot/docker/release/preview/windowsservercore/dependabot/windows/servercore-1909Copy head branch name to clipboard