ci: new workflow to update setup-texlive cache (#15)

* ci: new workflow to update setup-texlive cache

* drop the "List new cache" step

setup-texlive-action creates cache in the `runs.post` action.

* cleanup

* add gh doc links [ci skip]

.github/workflows/update-cache.yml

@@ -0,0 +1,35 @@
+name: Update cache
+
+on:
+  schedule:
+    # at 11:31 UTC (19:31 CST/UTC +8) on every Friday
+    # https://crontab.guru/#31_11_*_*_5
+    - cron: "31 11 * * 5"
+  workflow_dispatch:
+
+jobs:
+  update-cache:
+    runs-on: ubuntu-latest
+    permissions:
+      actions: write
+    steps:
+    - uses: actions/checkout@v4
+
+    # https://cli.github.com/manual/gh_cache_list
+    # https://cli.github.com/manual/gh_cache_delete
+    - name: Delete setup-texlive-action caches
+      run: |
+        cache_keys=$(\
+            gh cache list --key setup-texlive --json key --jq '.[].key')
+        for key in $cache_keys; do
+            echo "Deleting cache $key"
+            gh cache delete "$key"
+        done
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+    - name: Create new cache
+      uses: teatimeguest/setup-texlive-action@v3
+      with:
+        package-file: .github/tl_packages
+        update-all-packages: true