ENV：
target url ： set-cookie：admin＝abc
sqlmap： --cookie "admin=abc" -p admin --level 2

in lib.request.basic.forgeHeaders
when kb.mergeCookies is set True by default,
payloads in cookie will be override in code below:

if kb.mergeCookies:
    _ = lambda x: re.sub(r"(?i)\b%s=[^%s]+" % (re.escape(cookie.name), conf.cookieDel or DEFAULT_COOKIE_DELIMITER), "%s=%s" % (cookie.name, getUnicode(cookie.value)), x)
    headers[HTTP_HEADER.COOKIE] = _(headers[HTTP_HEADER.COOKIE])

payload will not in headers[HTTP_HEADER.COOKIE] and sql injection check will be failed.

Try merge cookie with default input 'N' can detect the injection