upgrades: prefix the logs with the filename for debugging

forgejo/upgrades/test-upgrade.sh

@@ -143,8 +143,8 @@ function start_forgejo() {
     local work_path=$DIR/forgejo-work-path
     daemon --chdir=$DIR --unsafe --env="TERM=$TERM" --env="HOME=$HOME" --env="PATH=$PATH" --pidfile=$DIR/forgejo-pid --errlog=$DIR/forgejo-err.log --output=$DIR/forgejo-out.log -- $DIR/forgejo-$version --config $work_path/app.ini --work-path $work_path
     if ! retry grep 'Starting server on' $work_path/log/forgejo.log ; then
-        cat $DIR/*.log
-        cat $work_path/log/*.log
+        grep '' $DIR/*.log
+        grep '' $work_path/log/*.log 2> /dev/null
         return 1
     fi
     create_user $version