DOC: Fixup the description of the -x509_strict option

DOC: Fixup the description of the -x509_strict option

POD commands must always be surrounded by blank lines

POD transformers read everything in paragraph mode.  The following
lines become *one* command, where the second line becomes part of the
text of the first, including the command itself.  In other words,
this:

    =item something
    =item something else

Translates to this in a man-page:

    something =item something else

Reviewed-by: David von Oheimb <david.von.oheimb@siemens.com>
(Merged from https://github.com/openssl/openssl/pull/13412)