patch 9.1.1807: :set doesn't clear local insecure flag like :setlocal does

patch 9.1.1807: :set doesn't clear local insecure flag like :setlocal does

Problem:  :set doesn't clear local insecure flag like :setlocal does.
Solution: Also clear the local insecure flag when using :set (zeertzjq).

This applies to local options like 'wrap', 'foldtext' and 'foldexpr',
whose global flags are actually never used.  For global-local options
like 'statusline' the behavior is already correct, so add some tests.

related: #18434

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>