Set Setpgid on child git processes (#19865) (#19881)

modules/markup/external/external.go

@@ -119,6 +119,8 @@ func (p *Renderer) Render(ctx *markup.RenderContext, input io.Reader, output io.
 		cmd.Stdin = input
 	}
 	cmd.Stdout = output
+	process.SetSysProcAttribute(cmd)
+
 	if err := cmd.Run(); err != nil {
 		return fmt.Errorf("%s render run command %s %v failed: %v", p.Name(), commands[0], args, err)
 	}