fix: Only update workspace LastUsed when the connection payload has changed (#4115)

This was causing every workspace to update last used to time.Now() when
coderd was restarted!

coderd/database/databasefake/databasefake.go

@@ -159,6 +159,33 @@ func (q *fakeQuerier) InsertAgentStat(_ context.Context, p database.InsertAgentS
 	return stat, nil
 }
 
+func (q *fakeQuerier) GetLatestAgentStat(_ context.Context, agentID uuid.UUID) (database.AgentStat, error) {
+	q.mutex.RLock()
+	defer q.mutex.RUnlock()
+
+	found := false
+	latest := database.AgentStat{}
+	for _, agentStat := range q.agentStats {
+		if agentStat.AgentID != agentID {
+			continue
+		}
+		if !found {
+			latest = agentStat
+			found = true
+			continue
+		}
+		if agentStat.CreatedAt.After(latest.CreatedAt) {
+			latest = agentStat
+			found = true
+			continue
+		}
+	}
+	if !found {
+		return database.AgentStat{}, sql.ErrNoRows
+	}
+	return latest, nil
+}
+
 func (q *fakeQuerier) GetTemplateDAUs(_ context.Context, templateID uuid.UUID) ([]database.GetTemplateDAUsRow, error) {
 	q.mutex.Lock()
 	defer q.mutex.Unlock()