c/agent: do not stop retrying heartbeats

There is nothing better to do other than infinitely retrying.

Change-Id: Ifda7e8d95120801f95f6fcf71124597cff086625
Reviewed-on: https://review.monogon.dev/c/monogon/+/1558
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
Tested-by: Jenkins CI
diff --git a/cloud/agent/agent.go b/cloud/agent/agent.go
index 131a38e..e6722d5 100644
--- a/cloud/agent/agent.go
+++ b/cloud/agent/agent.go
@@ -110,6 +110,8 @@
 	var installationReport *bpb.OSInstallationReport
 	var installationGeneration int64
 	b := backoff.NewExponentialBackOff()
+	// Never stop retrying, there is nothing else to do
+	b.MaxElapsedTime = 0
 	// Main heartbeat loop
 	for {
 		req := bpb.AgentHeartbeatRequest{