Avoid opening multiple PRs for pre-commit updates

This moves pre-commit updates to a github action that runs monthly.
This has the advantage of including *all* updates in a single PR.

.github/workflows/pre-commit-autoupdate.yml

@@ -0,0 +1,44 @@
+name: pre-commit autoupdate
+
+on:
+  schedule:
+  - cron: 0 0 1 * *  # first day of the month
+  workflow_dispatch:
+
+jobs:
+  pre-commit-autoupdate:
+    name: Update pre-commit hooks
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Python
+      uses: actions/setup-python@v4
+      with:
+          python-version-file: '.python-version'
+          check-latest: true
+
+    - name: Upgrade `pip`
+      run: python -m pip install --upgrade pip
+
+    - name: Install pre-commit
+      run: pip install pre-commit
+
+    - name: Update pre-commit hooks
+      run: pre-commit autoupdate
+
+    - name: Open a pull request
+      id: create-pr
+      uses: peter-evans/create-pull-request@v5
+      with:
+        add-paths: .pre-commit-config.yaml
+        commit-message: '[pre-commit] automatic update'
+        title: '[pre-commit] automatic update'
+        body: ''
+
+    - name: Enable pull request automerge
+      if: steps.create-pr.outputs.pull-request-operation == 'created'
+      uses: peter-evans/enable-pull-request-automerge@v3
+      with:
+        pull-request-number: ${{ steps.create-pr.outputs.pull-request-number }}
+        merge-method: squash

renovate.json

@@ -3,13 +3,9 @@
   "extends": [
     "config:base"
   ],
-  "pre-commit": {
-    "enabled": true
-  },
   "packageRules": [
     {
       "matchFileNames": [
-        ".pre-commit-config.yaml",
         ".github/workflows/**"
       ],
       "automerge": true,