Fix: fetch PR commits in ci check

scripts/ci-check-charon-pin-is-forward.sh

@@ -8,6 +8,10 @@ echo "This PR updates the charon pin from $OLD_CHARON_PIN to $NEW_CHARON_PIN"
 git clone https://github.com/AeneasVerif/charon
 cd charon
 
+# Fetch commits in PRs
+git config remote.origin.fetch "+refs/pull/*/head:refs/remotes/origin/pr/*"
+git fetch --all
+
 if ! git merge-base --is-ancestor "$OLD_CHARON_PIN" "$NEW_CHARON_PIN"; then
     echo "Error: the new charon pin does not have the old one as its ancestor. The pin must only move forward."
     exit 1