(maint) Add Equifax cert for pmt acceptance

The forge SSL certificates are being updated to use SHA-256, and that's
introduced a new certificate dependency that's not present on Windows.
Add it as part of acceptance testing. This is a stop-gap until the PMT
is fixed to come with its own certs.
Merge pull request #3320 from MikaelSmith/maint/master/fix-acceptance-cert

(maint) Add Equifax cert for pmt acceptance