crypto/x509: add new FreeBSD 12.2+ trusted certificate folder

[lapo-luchini]

Up to FreeBSD 12.1 the package ca_root_nss was needed in order to have
certificates under /usr/local/share/certs as the base system didn't have
a system trusted certificate store.

This has been fixed in FreeBSD 12.2 using /etc/ssl/certs:
https://svnweb.freebsd.org/base?view=revision&revision=357082

Fixes #46284

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[lapo-luchini]

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