Try to fix issue webfactory#20 with the proposed fix by @rieschl

index.js

@@ -20,6 +20,12 @@ try {
     fs.appendFileSync(`${homeSsh}/known_hosts`, '\ngithub.com ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAq2A7hRGmdnm9tUDbO9IDSwBK6TbQa+PXYPCPy6rbTrTtw7PHkccKrpp0yVhp5HdEIcKr6pLlVDBfOLX9QUsyCOV0wzfjIJNlGEYsdlLJizHhbn2mUjvSAHQqZETYP81eFzLQNnPHt4EVVUh7VfDESU84KezmD5QlWpXLmvU31/yMf+Se8xhHTvKSCZIFImWwoG6mbUoWf9nzpIoaSjB+weqqUUmpaaasXVal72J+UX2B+2RPW3RcT0eOzQgqlJL3RKrTJvdsjE3JEAvGq3lGHSZXy28G3skua2SmVi/w4yCE6gbODqnTWlg7+wC604ydGXA8VJiS5ap43JXiUFFAaQ==\n');
     fs.appendFileSync(`${homeSsh}/known_hosts`, '\ngithub.com ssh-dss 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\n');
 
+    if(fs.existsSync('/.dockerenv') && child_process.execFileSync('id', ['-u']).toString().trim() === '0') {
+        console.log("Running as root in docker container, copy known_hosts to /root/.ssh/known_hosts");
+        fs.mkdirSync('/root/.ssh', { recursive: true});
+        fs.copyFileSync(`${homeSsh}/known_hosts`, '/root/.ssh/known_hosts');
+    }
+
     console.log("Starting ssh-agent");
     const authSock = core.getInput('ssh-auth-sock');
     let sshAgentOutput = ''