This test was accidentally passing the value 2048 into the keytype
parameter of PKCS12_create, not the mac_iter parameter (because it had
one too many `nil`s in the call). This value is invalid, and will make
OpenSSL perform an out-of-bounds read which is caught when compiling
with ASAN.

This commit fixes the tests, and also adds some validation to
PKCS12.create to make sure any keytype passed is actually valid. Since
there only two valid keytype constants, and the whole feature is an
export-grade crypto era thing only ever supported by old MSIE, it seems
far more likely that code in the whild is using keytype similarly by
mistake rather than as intended. So this validation might catch that.

https://github.com/ruby/openssl/commit/47028686d2