MNT: Use hash for Action workflow versions and update, and add dependabot, if needed

.github/dependabot.yml

@@ -0,0 +1,16 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions" # See documentation for possible values
+    directory: ".github/workflows" # Location of package manifests
+    schedule:
+      interval: "monthly"
+    groups:
+      actions:
+        patterns:
+          - "*"
+

.github/workflows/publish-to-pypi.yml

@@ -19,8 +19,8 @@ jobs:
 
           # Check out the commit containing this workflow file.
           - name: checkout repo
-            uses: actions/checkout@v2
+            uses: actions/checkout@d632683dd7b4114ad314bca15554477dd762a938  # v4.2.0
 
           - name: custom action
-            uses: spacetelescope/action-publish_to_pypi@master
+            uses: spacetelescope/action-publish_to_pypi@db1a5633a75b441416f9bf6790ae78fb5f3bf970  # 1.2.4
             id: custom_action_0