gnutls: fix empty trust store (#81851)
gnutls: fix empty trust store (#81851)

Due to [1] gnutls may drop the whole trust store if there's at least one
certificate with duplicating extensions. I'm not 100% sure but most
likely macOS may have "com.apple.kerberos.kdc" certificate to be of such
kind. So let's filter them out when building trust store.

[1] https://gitlab.com/gnutls/gnutls/-/issues/1255

(#81022)
stgraber/homebrew-core,uyjulian/homebrew-core,zyedidia/homebrew-core,nandub/homebrew-core,sjackman/homebrew-core,makigumo/homebrew-core,Moisan/homebrew-core,makigumo/homebrew-core,Moisan/homebrew-core,cblecker/homebrew-core,lemzwerg/homebrew-core,chrisfinazzo/homebrew-core,lemzwerg/homebrew-core,nandub/homebrew-core,mfikes/homebrew-core,chrisfinazzo/homebrew-core,stgraber/homebrew-core,mfikes/homebrew-core,Homebrew/homebrew-core,adam-moss/homebrew-core,filcab/homebrew-core,Homebrew/homebrew-core,uyjulian/homebrew-core,sjackman/homebrew-core,nbari/homebrew-core,nbari/homebrew-core,adam-moss/homebrew-core,filcab/homebrew-core,zyedidia/homebrew-core,cblecker/homebrew-core