patch 8.2.0156: various typos in source files and tests

Problem:    Various typos in source files and tests.
Solution:   Fix the typos. (Emir Sari, closes #5532)
diff --git a/src/getchar.c b/src/getchar.c
index 72ddbb9..d056bcc 100644
--- a/src/getchar.c
+++ b/src/getchar.c
@@ -3237,7 +3237,7 @@
  *	1. a scriptfile
  *	2. the keyboard
  *
- *  As much characters as we can get (upto 'maxlen') are put in "buf" and
+ *  As many characters as we can get (up to 'maxlen') are put in "buf" and
  *  NUL terminated (buffer length must be 'maxlen' + 1).
  *  Minimum for "maxlen" is 3!!!!
  *