Set fixed container versions

To avoid redownloading every second time the pipeline runs

algo2/pairingheap.c

@@ -166,7 +166,7 @@ int main() {
     struct PHeap ph;
     ph_init(&ph);
 
-    for (int i = 0; i < 20; i++) {
+    for (int i = 0; i < 15; i++) {
         ph_insert_malloc(&ph, rand() % 100);
     }