Use the make task in Github Actions

Briefly the `generate-fake-stemcell-automation` task was a no-op on
windows because of issues with the CI setup. This has been resolved so
we can now use this target on Windows OS workers.

Signed-off-by: Brian Cunnie <bcunnie@vmware.com>

.github/workflows/go.yml

@@ -17,7 +17,7 @@ jobs:
         go-version-file: go.mod
     - name: Provide `StemcellAutomation.zip` for `go:embed` consumption in `assets` package
       run: |
-        cp integration/construct/assets/StemcellAutomation.zip assets/
+        make generate-fake-stemcell-automation
     - uses: golangci/golangci-lint-action@v3
       if: ${{ matrix.os == 'windows-2019' }}
     - uses: golangci/golangci-lint-action@v3