fully pinned github actions

Author: nedbat

.github/dependabot.yml

@@ -0,0 +1,21 @@
+# From:
+# https://docs.github.com/en/code-security/supply-chain-security/keeping-your-dependencies-updated-automatically/keeping-your-actions-up-to-date-with-dependabot
+# Set update schedule for GitHub Actions
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      # Check for updates to GitHub Actions once a week
+      interval: "weekly"
+      day: "sunday"
+    cooldown:
+      # https://blog.yossarian.net/2025/11/21/We-should-all-be-using-dependency-cooldowns
+      default-days: 7
+    groups:
+      action-dependencies:
+        patterns:
+          - "*"
+    commit-message:
+      prefix: "chore"

.github/workflows/tests.yml

@@ -50,12 +50,12 @@ jobs:
 
     steps:
       - name: "Check out the repo"
-        uses: "actions/checkout@v4"
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
         with:
           persist-credentials: false
 
       - name: "Set up Python"
-        uses: "actions/setup-python@v5"
+        uses: actions/setup-python@83679a892e2d95755f2dac6acb0bfd1e9ac5d548 # v6.1.0
         with:
           python-version: "${{ matrix.python-version }}"
           allow-prereleases: true
@@ -87,12 +87,12 @@ jobs:
 
     steps:
       - name: "Check out the repo"
-        uses: "actions/checkout@v4"
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
         with:
           persist-credentials: false
 
       - name: "Set up Python"
-        uses: "actions/setup-python@v5"
+        uses: actions/setup-python@83679a892e2d95755f2dac6acb0bfd1e9ac5d548 # v6.1.0
         with:
           python-version: "3.10"