Mint GitHub App token in push workflow (#551)

Replace the expired POLICYENGINE_GITHUB PAT with a short-lived
GitHub App token (APP_ID / APP_PRIVATE_KEY) in the versioning and
Deploy jobs. Each job generates its own token since App tokens do
not cross job boundaries. Matches the pattern in policyengine-core
PR #470 and microdf PR #296.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: MaxGhenis

.github/workflows/push.yaml

@@ -26,10 +26,16 @@ jobs:
       && !(github.event.head_commit.message == 'Update PolicyEngine Canada')
     runs-on: ubuntu-latest
     steps:
+      - name: Generate GitHub App token
+        id: app-token
+        uses: actions/create-github-app-token@v1
+        with:
+          app-id: ${{ secrets.APP_ID }}
+          private-key: ${{ secrets.APP_PRIVATE_KEY }}
       - name: Checkout repo
         uses: actions/checkout@v4
         with:
-          token: ${{ secrets.POLICYENGINE_GITHUB }}
+          token: ${{ steps.app-token.outputs.token }}
       - name: Setup Python
         uses: actions/setup-python@v5
         with:
@@ -49,6 +55,8 @@ jobs:
           committer_name: Github Actions[bot]
           author_name: Github Actions[bot]
           message: Update PolicyEngine Canada
+          github_token: ${{ steps.app-token.outputs.token }}
+          fetch: false
   Test:
     runs-on: ${{ matrix.os }}
     if: |
@@ -111,13 +119,17 @@ jobs:
       (github.repository == 'PolicyEngine/policyengine-canada')
       && (github.event.head_commit.message == 'Update PolicyEngine Canada')
     runs-on: ubuntu-latest
-    env:
-      GH_TOKEN: ${{ secrets.POLICYENGINE_GITHUB }}
     steps:
+      - name: Generate GitHub App token
+        id: app-token
+        uses: actions/create-github-app-token@v1
+        with:
+          app-id: ${{ secrets.APP_ID }}
+          private-key: ${{ secrets.APP_PRIVATE_KEY }}
       - name: Checkout repo
         uses: actions/checkout@v4
         with:
-          token: ${{ secrets.POLICYENGINE_GITHUB }}
+          token: ${{ steps.app-token.outputs.token }}
       - name: Setup Python
         uses: actions/setup-python@v5
         with:
@@ -130,4 +142,4 @@ jobs:
       - name: Update API
         run: python .github/update_api.py
         env:
-          GITHUB_TOKEN: ${{ secrets.POLICYENGINE_GITHUB }}
+          GITHUB_TOKEN: ${{ steps.app-token.outputs.token }}

changelog.d/fixed/migrate-to-app-token.md

@@ -0,0 +1 @@
+Migrated push workflow from the expired `POLICYENGINE_GITHUB` PAT to a short-lived GitHub App token (`APP_ID` / `APP_PRIVATE_KEY`), so the `versioning` job can push the "Update PolicyEngine Canada" commit that triggers Test, Publish, and Deploy. Matches the pattern already used by policyengine-core, policyengine-us, and microdf.