Simplify get_programs(), specify a real Preview activation epoch for new BPFLoader (#11930)

(cherry picked from commit f385af25e5)

Co-authored-by: Michael Vines <mvines@gmail.com>

runtime/src/bank.rs

@@ -2647,7 +2647,7 @@ impl Bank {
             assert!(callback_w.is_none(), "Already callback has been initiated");
             *callback_w = Some(entered_epoch_callback);
         }
-        // immedaitely fire the callback as initial invocation
+        // immediately fire the callback as initial invocation
         self.reinvoke_entered_epoch_callback(true);
     }