Don't try to login to quay if a push is made by dependabot

Dependabot based push/pr builds don't have access to the quay secrets
it seems (github magic?) (see [1], [2]) so lets avoid it all together.
Dependabot pushes/PRs can be recognized by the github.actor value according
to the GitHub docs[3].

Fixes #92

[1]: #89
[2]: #95
[3]: https://docs.github.com/en/code-security/supply-chain-security/keeping-your-dependencies-updated-automatically/automating-dependabot-with-github-actions#handling-pull_request-events

Signed-off-by: Manuel Mendez <mmendez@equinix.com>

Author: mmlb

.github/workflows/kernel-push.yaml

@@ -12,6 +12,7 @@ jobs:
       uses: actions/checkout@v2.3.5
 
     - name: Login to quay.io
+      if: ${{ github.actor == "dependabot[bot]" }}
       uses: docker/login-action@v1
       with:
         registry: quay.io

.github/workflows/push.yaml

@@ -1,6 +1,8 @@
 name: For each commit
 on:
   push:
+    branches:
+    - main
     paths-ignore:
     - kernel/**
 jobs:
@@ -18,6 +20,7 @@ jobs:
       uses: docker/setup-buildx-action@v1.3.0
 
     - name: Login to quay.io
+      if: ${{ github.actor == "dependabot[bot]" }}
       uses: docker/login-action@v1
       with:
         registry: quay.io