patch 8.2.3637: typos in test files

Problem:    Typos in test files.
Solution:   Correct the typos. (Dominique Pellé, closes #9175)
diff --git a/src/testdir/test_recover.vim b/src/testdir/test_recover.vim
index d012974..362ddb0 100644
--- a/src/testdir/test_recover.vim
+++ b/src/testdir/test_recover.vim
@@ -361,7 +361,7 @@
 endfunc
 
 " Test for :recover using a unreadable swap file
-func Test_recover_unreadble_swap_file()
+func Test_recover_unreadable_swap_file()
   CheckUnix
   CheckNotRoot
   new Xfile1