ci: fix release commit check

ci/check_release_commit_messages.sh

@@ -2,6 +2,8 @@
 
 fail=0
 
+git fetch origin master
+
 # list all commits between HEAD and master
 for commit in $(git rev-list origin/master..)
 do

ci/prebuild.yml

@@ -37,6 +37,10 @@ gen prebuild:
 
 release commit messages prebuild:
   stage: prebuild
+  before_script: []  # nothing needed
+  variables:
+    # We need to clone the repo properly so we can work with origin/master
+    GIT_STRATEGY: clone
   only:
     - /^release\//
   script: