Revert "github actions: use per-repository token for automatic package updates workflow"

This reverts commit fc95ff7881.

Unfortunately GITHUB_TOKEN authentication cannot start other action
(recent automatic update pushes haven't been built), so switch back to
a new personal access token (generated by me).

Ref: https://stackoverflow.com/a/67551255

.github/workflows/package_updates.yml

@@ -14,10 +14,10 @@ jobs:
       uses: actions/checkout@v2
       with:
         fetch-depth: 0
-        token: ${{ secrets.GITHUB_TOKEN }}
+        token: ${{ secrets.GH_API_KEY }}
     - name: Process package updates
       env:
-        GITHUB_API_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        GITHUB_API_TOKEN: ${{ secrets.GH_API_KEY }}
         BUILD_PACKAGES: "true"
         GIT_COMMIT_PACKAGES: "true"
         GIT_PUSH_PACKAGES: "true"