patch 9.0.1453: typos in source code and tests

Problem:    Typos in source code and tests.
Solution:   Fi the typos. (Dominique Pellé, closes #12217)
diff --git a/src/logfile.c b/src/logfile.c
index 673468e..999acf0 100644
--- a/src/logfile.c
+++ b/src/logfile.c
@@ -9,7 +9,7 @@
 /*
  * Implements logging.  Originally intended for the channel feature, which is
  * why the "ch_" prefix is used.  Also useful for any kind of low-level and
- * async debuging.
+ * async debugging.
  */
 
 #include "vim.h"