logs: always prefix with the file name

otherwise it is difficult to figure out where the runner logs end and
where the forgejo logs start.

lib/lib.sh

@@ -297,9 +297,9 @@ function show_logs() {
     (
 	cd $DIR
 	set +e
-        grep --text '' *.log
+        grep --with-filename --text '' *.log
-        grep --text '' forgejo-work-path/log/*.log
+        grep --with-filename --text '' forgejo-work-path/log/*.log
-	grep --text '' *.out
+	grep --with-filename --text '' *.out
     )
 }