Only push images from bitnami/minideb repository

Make it so that only builds triggered by the `bitnami/minideb`
repository will attempt to push images (because it is the only
repository that has access to the required secrets). This will prevent
builds in forked repositories that don't have access to the secrets from
failing.

.github/workflows/main.yml

@@ -56,7 +56,7 @@ jobs:
           platform: "${{ matrix.arch }}"
           is_latest: ${{ matrix.dist == env.LATEST }}
       - name: Push
-        if: github.ref == 'refs/heads/master'
+        if: github.repository == 'bitnami/minideb' && github.ref == 'refs/heads/master'
         env:
           DOCKER_USERNAME: ${{ secrets.DOCKER_USERNAME }}
           DOCKER_PASSWORD: ${{ secrets.DOCKER_PASSWORD }}
@@ -71,7 +71,7 @@ jobs:
   deploy_manifests:
     runs-on: ubuntu-22.04
     needs: [ build_multiarch ]
-    if: github.ref == 'refs/heads/master'
+    if: github.repository == 'bitnami/minideb' && github.ref == 'refs/heads/master'
     env:
       DOCKER_USERNAME: ${{ secrets.DOCKER_USERNAME }}
       DOCKER_PASSWORD: ${{ secrets.DOCKER_PASSWORD }}
@@ -89,7 +89,7 @@ jobs:
     needs:
       - build_multiarch
       - deploy_manifests
-    if: always()
+    if: github.repository == 'bitnami/minideb'
     name: Notify unsuccessful CI run
     steps:
       - name: Notify in Slack channel