chore: add 'slideshow' to spell-check expect list

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: catol-abacus

.github/actions/spell-check/expect.txt

@@ -1442,6 +1442,7 @@ SKEXP
 SKIPOWNPROCESS
 sku
 SLGP
+slideshow
 sln
 SMALLICON
 smartphone