MM-43848: Fix flaky TestUserStore/LocalCache+MySQL/UpdateUpdateAt (#20139)

Because of the fact that t.Unix() family of methods do not
contain the monotonic time, there is no guarantee that
consecutive methods will increase in time.

This is more of a best effort to double the time slept,
but in reality there is no way to control this unless
you specifically control your servers, which is hard to achieve
in a CI environment.

https://mattermost.atlassian.net/browse/MM-43848

```release-note
NONE
```

store/storetest/file_info_store.go

@@ -635,7 +635,7 @@ func testFileInfoStoreGetFilesBatchForIndexing(t *testing.T, ss store.Store) {
 	defer func() {
 		ss.FileInfo().PermanentDelete(f1.Id)
 	}()
-	time.Sleep(1 * time.Millisecond)
+	time.Sleep(2 * time.Millisecond)
 
 	o2 := &model.Post{}
 	o2.ChannelId = c2.Id
@@ -653,7 +653,7 @@ func testFileInfoStoreGetFilesBatchForIndexing(t *testing.T, ss store.Store) {
 	defer func() {
 		ss.FileInfo().PermanentDelete(f2.Id)
 	}()
-	time.Sleep(1 * time.Millisecond)
+	time.Sleep(2 * time.Millisecond)
 
 	o3 := &model.Post{}
 	o3.ChannelId = c1.Id

store/storetest/group_store.go

@@ -1120,7 +1120,7 @@ func testUpsertMember(t *testing.T, ss store.Store) {
 
 	// Duplicate composite key (GroupId, UserId)
 	// Ensure new CreateAt > previous CreateAt for the same (groupId, userId)
-	time.Sleep(1 * time.Millisecond)
+	time.Sleep(2 * time.Millisecond)
 	_, err = ss.Group().UpsertMember(group.Id, user.Id)
 	require.NoError(t, err)
 
@@ -1131,7 +1131,7 @@ func testUpsertMember(t *testing.T, ss store.Store) {
 
 	// Restores a deleted member
 	// Ensure new CreateAt > previous CreateAt for the same (groupId, userId)
-	time.Sleep(1 * time.Millisecond)
+	time.Sleep(2 * time.Millisecond)
 	_, err = ss.Group().UpsertMember(group.Id, user.Id)
 	require.NoError(t, err)
 
@@ -1186,7 +1186,7 @@ func testUpsertMembers(t *testing.T, ss store.Store) {
 
 	// Duplicate composite key (GroupId, UserId)
 	// Ensure new CreateAt > previous CreateAt for the same (groupId, userId)
-	// time.Sleep(1 * time.Millisecond)
+	// time.Sleep(2 * time.Millisecond)
 	_, err = ss.Group().UpsertMembers(group.Id, []string{user.Id})
 	require.NoError(t, err)
 
@@ -1197,7 +1197,7 @@ func testUpsertMembers(t *testing.T, ss store.Store) {
 
 	// Restores a deleted member
 	// Ensure new CreateAt > previous CreateAt for the same (groupId, userId)
-	time.Sleep(1 * time.Millisecond)
+	time.Sleep(2 * time.Millisecond)
 	_, err = ss.Group().UpsertMembers(group.Id, []string{user.Id, user2.Id})
 	require.NoError(t, err)
 

store/storetest/shared_channel_store.go

@@ -1189,7 +1189,7 @@ func testUpsertSharedChannelAttachment(t *testing.T, ss store.Store) {
 		require.NoError(t, err, "couldn't save shared channel attachment", err)
 
 		// make sure enough time passed that GetMillis returns a different value
-		time.Sleep(1 * time.Millisecond)
+		time.Sleep(2 * time.Millisecond)
 
 		_, err = ss.SharedChannel().UpsertAttachment(saved)
 		require.NoError(t, err, "couldn't upsert shared channel attachment", err)

store/storetest/thread_store.go

@@ -858,7 +858,7 @@ func testVarious(t *testing.T, ss store.Store) {
 	viewThread(user1ID, dm1post1.Id)
 
 	// Add reply to a viewed thread to confirm it's unread again.
-	time.Sleep(1 * time.Millisecond)
+	time.Sleep(2 * time.Millisecond)
 	threadStoreCreateReply(t, ss, team1channel1.Id, team1channel1post2.Id, user2ID, model.GetMillis())
 
 	// Actually make team2channel1post2deleted deleted

store/storetest/upload_session_store.go

@@ -158,7 +158,7 @@ func testUploadSessionStoreGetForUser(t *testing.T, ss store.Store) {
 		require.NotNil(t, us)
 		require.NotEmpty(t, us)
 		// We need this to make sure the ordering is consistent.
-		time.Sleep(1 * time.Millisecond)
+		time.Sleep(2 * time.Millisecond)
 	}
 
 	t.Run("should return existing sessions", func(t *testing.T) {

store/storetest/user_store.go

@@ -236,7 +236,6 @@ func testUserStoreUpdate(t *testing.T, ss store.Store) {
 }
 
 func testUserStoreUpdateUpdateAt(t *testing.T, ss store.Store) {
-	t.Skip("MM-43848")
 	u1 := &model.User{}
 	u1.Email = MakeEmail()
 	_, err := ss.User().Save(u1)
@@ -246,7 +245,7 @@ func testUserStoreUpdateUpdateAt(t *testing.T, ss store.Store) {
 	require.NoError(t, nErr)
 
 	// Ensure UpdateAt has a change to be different below.
-	time.Sleep(1 * time.Millisecond)
+	time.Sleep(2 * time.Millisecond)
 
 	_, err = ss.User().UpdateUpdateAt(u1.Id)
 	require.NoError(t, err)