fix flaky test

pkg/solana/logpoller/loader_test.go

@@ -110,6 +110,18 @@ func TestEncodedLogCollector_BackfillForAddress(t *testing.T) {
 		_, _ = rand.Read(sigs[idx][:])
 	}
 
+	// GetLatestBlockhash might be called at start-up; make it take some time because the result isn't needed for this test
+	client.EXPECT().GetLatestBlockhash(mock.Anything, mock.Anything).Return(&rpc.GetLatestBlockhashResult{
+		RPCContext: rpc.RPCContext{
+			Context: rpc.Context{
+				Slot: slots[0],
+			},
+		},
+		Value: &rpc.LatestBlockhashResult{
+			LastValidBlockHeight: 42,
+		},
+	}, nil).After(2 * time.Second).Maybe()
+
 	client.EXPECT().
 		GetSignaturesForAddressWithOpts(mock.Anything, pubKey, mock.MatchedBy(func(opts *rpc.GetSignaturesForAddressOpts) bool {
 			return opts != nil && opts.Before.String() == solana.Signature{}.String()