deploy: allow deploying in forks

It would be nice if we could deploy the Azure Function contingent on the
presence of the `AZURE_RBAC_CREDENTIALS` secret. However, this is not
possible in GitHub workflows: the job-level `if:` conditions lack access
to the `secrets` context. Strangely enough, they _do_ have access to the
`vars` context...

So let's allow deploying in forks by requiring both the
`AZURE_RBAC_CREDENTIALS` secret as well as a repository _variable_
called `DEPLOY_TO_AZURE` that needs to be set to `true`.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/deploy.yml

@@ -11,7 +11,7 @@ on:
 
 jobs:
   deploy:
-    if: github.event.repository.fork == false
+    if: github.event.repository.fork == false || vars.DEPLOY_TO_AZURE == 'true'
     environment: deploy-to-azure
     runs-on: ubuntu-latest
     steps: