fix: unshallow a clone for diff

entrypoint.sh

@@ -2,6 +2,11 @@
 
 set -eu
 
+# Github by default does shallow clones, where there is only one single commit
+# which adds everything.  In this action I’m only trying to check what was
+# /added/ in this commit, not the entire repo, so we need the diff with the
+# previous version.
+git fetch --deepen=2
 # This works for pull_request and push because on a pr github actions will
 # create a synthetic merge commit and run the action on that, so this
 # encompasses the entire potential merge.