security/rubygem-ruby-saml: Update to 1.12.2.

This upgrade is required for gitlab-ce 13.10.3 security update.

Changes: https://github.com/onelogin/ruby-saml/blob/master/changelog.md

MFH: 2021Q2
(cherry picked from commit e7761c8640b19f7cf8105c6dfbc9f4de9bb536cc)