diff --git a/.github/workflows/build-notebooks-TEMPLATE.yaml b/.github/workflows/build-notebooks-TEMPLATE.yaml
index e7b804d07..13ff9ae13 100644
--- a/.github/workflows/build-notebooks-TEMPLATE.yaml
+++ b/.github/workflows/build-notebooks-TEMPLATE.yaml
@@ -78,6 +78,8 @@ jobs:
       - name: "pull_request: make ${{ inputs.target }}"
         run: |
           # start a black hole container registry as make target always does a push
+          mkdir -p $HOME/.config/containers/registries.conf.d/
+          cp ci/insecure_localhost_registry.conf $HOME/.config/containers/registries.conf.d/insecure_localhost_registry.conf
           go run ci/dev_null_container_registry.go &
           # build and push the image
           make ${{ inputs.target }}
diff --git a/.github/workflows/build-notebooks-pr.yaml b/.github/workflows/build-notebooks-pr.yaml
index e1380370a..12eb52780 100644
--- a/.github/workflows/build-notebooks-pr.yaml
+++ b/.github/workflows/build-notebooks-pr.yaml
@@ -1,5 +1,5 @@
 ---
-"name": "Build Notebooks",
+"name": "Build Notebooks"
 "permissions":
   "packages": "read"
 "on":
@@ -13,16 +13,17 @@ jobs:
       matrix: ${{ steps.gen.outputs.matrix }}
     steps:
       - uses: actions/checkout@v4
-      - run: python3 gen_gha_matrix_jobs.py
+      - run: python3 ci/gen_gha_matrix_jobs.py
         id: gen
 
   # base images
   build:
-    needs: [ "gen" ]
+    needs: ["gen"]
     strategy:
       fail-fast: false
       matrix: "${{ fromJson(needs.gen.outputs.matrix) }}"
     uses: ./.github/workflows/build-notebooks-TEMPLATE.yaml
     with:
       target: "${{ matrix.target }}"
+      github: "${{ toJSON(github) }}"
     secrets: inherit
diff --git a/ci/gen_gha_matrix_jobs.py b/ci/gen_gha_matrix_jobs.py
index 8d766bb18..088535796 100644
--- a/ci/gen_gha_matrix_jobs.py
+++ b/ci/gen_gha_matrix_jobs.py
@@ -1,3 +1,4 @@
+import itertools
 import json
 import os
 import pathlib
@@ -110,18 +111,22 @@ def write_github_workflow_file(tree: dict[str, list[str]], path: pathlib.Path) -
         json.dump(workflow, f, sort_keys=False, indent=4)
         print(file=f)
 
+
+def flatten(list_of_lists):
+    return list(itertools.chain.from_iterable(list_of_lists))
+
 def compute_leafs_in_dependency_tree(tree: dict[str, list[str]]) -> list[str]:
     key_set = set(tree.keys())
-    value_set = set(*tree.values())
+    value_set = set(flatten(tree.values()))
     return [key for key in key_set if key not in value_set]
 
-def print_github_actions_pr_matrix(tree: dict[str, list[str]], leafs: list[str]) -> str:
+def print_github_actions_pr_matrix(tree: dict[str, list[str]], leafs: list[str]) -> list[str]:
     """Outputs GitHub matrix definition Json
     """
     targets = []
     for leaf in leafs:
         # in level 0, we only want base images, not other utility tasks
-        if not tree[leaf] and leaf.startswith("base-"):
+        if not tree[leaf] and not leaf.startswith("base-"):
             continue
 
         # we won't build rhel-based images because they need subscription
@@ -131,7 +136,7 @@ def print_github_actions_pr_matrix(tree: dict[str, list[str]], leafs: list[str])
         targets.append(leaf)
 
     matrix = {"target": targets}
-    return f"matrix={json.dumps(matrix, separators=(",", ":"))}"
+    return [f"matrix={json.dumps(matrix, separators=(',', ':'))}"]
 
 
 def main() -> None:
@@ -143,10 +148,9 @@ def main() -> None:
     write_github_workflow_file(tree, project_dir / ".github" / "workflows" / "build-notebooks.yaml")
 
     leafs = compute_leafs_in_dependency_tree(tree)
-    output = print_github_actions_pr_matrix(leafs)
-
-    write_github_workflow_file(tree)
+    output = print_github_actions_pr_matrix(tree, leafs)
 
+    print("leafs", leafs)
     print(*output, sep="\n")
     with open(os.environ["GITHUB_OUTPUT"], "at") as f:
         for line in output:
diff --git a/ci/insecure-localhost-registry.conf b/ci/insecure_localhost_registry.conf
similarity index 100%
rename from ci/insecure-localhost-registry.conf
rename to ci/insecure_localhost_registry.conf