patch 9.0.2135: No test for mode() when executing Ex commands

Problem:  No test for mode() when executing Ex commands
Solution: Add some test cases and simplify several other test cases.
          Also add a few more test cases for ModeChanged.

closes: #13588

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/evalfunc.c b/src/evalfunc.c
index fa27d0d..b0b9750 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -9733,7 +9733,7 @@
     if (in_vim9script() && check_for_string_arg(argvars, 0) == FAIL)
 	return;
 
-    // seting an environment variable may be dangerous, e.g. you could
+    // setting an environment variable may be dangerous, e.g. you could
     // setenv GCONV_PATH=/tmp and then have iconv() unexpectedly call
     // a shell command using some shared library:
     if (check_restricted() || check_secure())