Perform sanity tests on certificate data

Others are possible (and may be added later) but these would have caught the
recent bad update. This job is placed in the static_analysis stage, so will
slot neatly in when we add the common CI jobs.

.gitlab-ci.yml

+stages:
+  - static_analysis
+
+certdata:
+  stage: static_analysis
+  tags: [ cross ]
+  script:
+    - "# Checking CertData..."
+    - test $(stat -c%s Resources/files/CertData) -gt 1000
+    - test $(grep -- "-----BEGIN CERTIFICATE-----" Resources/files/CertData | wc -l) -gt 50
+    - "# CertData looks good"