patch 8.2.4611: typos in tests; one lua line not covered by test

Problem:    Typos in tests; one lua line not covered by test.
Solution:   Fix typos. Add test case. (Dominique Pellé, closes #9994)
diff --git a/src/testdir/test_spell.vim b/src/testdir/test_spell.vim
index 804c5de..94a072e 100644
--- a/src/testdir/test_spell.vim
+++ b/src/testdir/test_spell.vim
@@ -417,7 +417,7 @@
   bwipe!
 endfunc
 
-" Test for 'spellsuggest' expr errrors
+" Test for 'spellsuggest' expr errors
 func Test_spellsuggest_expr_errors()
   " 'spellsuggest'
   func MySuggest()