[ci] Set SSL_CERT_FILE variable for mac to point to the CA bundle

in order for davix to be able to read https

Author: dpiparo

.github/workflows/root-ci.yml

@@ -158,6 +158,7 @@ jobs:
         env:
           INCREMENTAL: ${{ !contains(github.event.pull_request.labels.*.name, 'clean build') }}
           GITHUB_PR_ORIGIN: ${{ github.event.pull_request.head.repo.clone_url }}
+          SSL_CERT_FILE: ${{ secrets.SSL_CERT_FILE_VALUE }} # necessary for davix to connect to https
         run: ".github/workflows/root-ci-config/build_root.py
                     --buildtype       RelWithDebInfo
                     --incremental     $INCREMENTAL