ci: Modernize GitHub Actions usage

* New variable structure for secrets access is simpler.
* Upstream luacov-coveralls has included my patch (but no release yet,
  so still installing from SCM rockspec)

.github/workflows/busted.yml

@@ -25,12 +25,12 @@ jobs:
       run: |
         luarocks install penlight ${{ matrix.penlightVersion }}
         luarocks install busted
-        luarocks install https://raw.githubusercontent.com/alerque/luacov-coveralls/master/rockspecs/luacov-coveralls-scm-0.rockspec
+        luarocks install https://raw.githubusercontent.com/moteus/luacov-coveralls/master/rockspecs/luacov-coveralls-scm-0.rockspec
     - name: Run Busted Tests
       run: busted -c -v
     - name: Report Test Coverage
       if: success()
       continue-on-error: true
       run: luacov-coveralls -i cassowary -e .luarocks
       env:
-        COVERALLS_REPO_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        COVERALLS_REPO_TOKEN: ${{ github.token }}