Appends follow-up UI fixes

[iethree]

Description

A couple little things came up during today's demo:

1. we should auto-select the only model to append if there's only 1
   

2. there was a bug where if you did certain things in the ui (like create a new question), we would re-trigger an error modal.

Tests

• tests have been added

[github-actions]

Codenotify: Notifying subscribers in CODENOTIFY files for diff 08b8dfb...e9f1400.

Notify	File(s)
@ranquild	frontend/src/metabase/status/components/FileUploadStatus/FileUploadStatus.tsx frontend/src/metabase/status/components/FileUploadStatus/FileUploadStatus.unit.spec.tsx

[replay-io]

Status	Complete ↗︎
Commit	e9f1400
Results	⚠️ 1 Flaky ✅ 2316 Passed

[mazameli]

we should auto-select the only model to append if there's only 1

IMO, if there are any to append to, we should just auto-select one of them, since even dumbly selecting the first one alphabetically has a higher probability of being the one the user intended (>0% chance of being right) than the probability that no selection is the correct one (exactly 0%, haha). If it's easy to be slightly smarter (like auto selecting the one with the most recent last_edited_at date or something), so much the better.

[iethree]

we should auto-select the only model to append if there's only 1

IMO, if there are any to append to, we should just auto-select one of them, since even dumbly selecting the first one alphabetically has a higher probability of being the one the user intended (>0% chance of being right) than the probability that no selection is the correct one (exactly 0%, haha). If it's easy to be slightly smarter (like auto selecting the one with the most recent last_edited_at date or something), so much the better.

ok, now this will auto-select the most recently update model (which will also be the only model if there's just one)

[iethree]

I named this function especially for @sloansparger

[sloansparger]

lgtm!