patchtest: Add test for deprecated CVE_CHECK_IGNORE

If a recipes was modified recommand the use of `CVE_STATUS` instead if
`CVE_CHECK_IGNORE` is used. This is a depreacted variable and will
result in a warning from the cve-check.class and should hence not be
used anymore. [YOCTO #15311]

Signed-off-by: Simone Weiß <simone.p.weiss@posteo.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>