patch 9.1.0220: Few typos in source and test files

Problem:  Typos in code and tests.
Solution: Fix typos (zeertzjq).

closes: #14321

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/vim9class.c b/src/vim9class.c
index b640323..6963491 100644
--- a/src/vim9class.c
+++ b/src/vim9class.c
@@ -3782,7 +3782,7 @@
 }
 
 /*
- * Calls the object "empty()" method and returns the method retun value.  In
+ * Calls the object "empty()" method and returns the method return value.  In
  * case of an error, returns TRUE.
  */
     int