fix: Use canonical shared decks URL (#5692)

## Linked issue (required)

Fixes #5691

## Summary / motivation (required)

Updates the **Get Shared** link to use the current `/shared/decks` URL
directly instead of `/shared/decks/`, which redirects to it.

## Steps to reproduce (required, use N/A if not applicable)

1. Open Anki's deck list.
2. Click **Get Shared**.
3. Observe that `/shared/decks/` is opened and redirects to
`/shared/decks`.

## How to test (required)

### Checklist (minimum)

- [x] I ran `./ninja check` or an equivalent relevant check locally.
- [ ] I added or updated tests when the change is non-trivial or
behavior changed.

### Details

Ran `./ninja check:pytest:aqt` successfully.

Manually verified that `/shared/decks/` redirects to `/shared/decks`,
and
that `/shared/decks` loads directly. No automated test was added because
this is a trivial one-line URL correction.

## Before / after behavior (optional)

Before: **Get Shared** opens `/shared/decks/` and relies on a redirect.

After: **Get Shared** opens `/shared/decks` directly.

## Risk / compatibility / migration (optional)

N/A. This is a one-line URL change.

## UI evidence (required for visual changes; otherwise N/A)

N/A

## Scope

- [x] This PR is focused on one change (no unrelated edits).

qt/aqt/deckbrowser.py

@@ -394,7 +394,7 @@ class DeckBrowser:
         )
 
     def _onShared(self) -> None:
-        openLink(f"{aqt.appShared}decks/")
+        openLink(f"{aqt.appShared}decks")
 
     def _on_create(self) -> None:
         if op := add_deck_dialog(