Split translation of learn in the deck list

Closes #2708

ftl/core/decks.ftl

@@ -30,3 +30,4 @@ decks-study = Study
 decks-study-deck = Study Deck
 decks-filtered-deck-search-empty = No cards matched the provided search. Some cards may have been excluded because they are in a different filtered deck, or suspended.
 decks-unmovable-cards = Show any excluded cards
+decks-learn-header = Learn

qt/aqt/deckbrowser.py

@@ -196,7 +196,7 @@ class DeckBrowser:
 <th class=count>{}</th>
 <th class=count>{}</th>
 <th class=optscol></th></tr>""".format(
-            tr.decks_deck(),
+            tr.decks_learn_header(),
             tr.actions_new(),
             tr.card_stats_review_log_type_learn(),
             tr.statistics_due_count(),