Fix serializer_EVP_PKEY_to_bio so that that the key is exported if the serializer...

Fix serializer_EVP_PKEY_to_bio so that that the key is exported if the serializer provider does not match the key provider.

RSA keys in the 'base' provider are different from a fips provider RSA key (since they have different object structures).
To use a fips provider key in the base serializer the key needs to be exported.
The fix was suggested by @levitte.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/12162)