test: add test case to reliably reproduce RAND leak during POST

The FIPS provider leaks a RAND if the POST is run at initialisation time.
This test case reliably reproduces this event.

test: add test case to reliably reproduce RAND leak during POST

The FIPS provider leaks a RAND if the POST is run at initialisation time.
This test case reliably reproduces this event.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15278)

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