Fix update krew-index job

- The job did not get triggered when the 0.17.1 release was created.
  We were using the "on push tags" event trigger however this seems to
  apply if "git push" is used. We actually use "gh release create" so
  we need to use the "on release published" event trigger (I verified
  this works via a test job on my fork).

- The krew-release-bot action failed b/c it could not find our .krew.yaml
  file. We need to first check out the "releases" repository.

Signed-off-by: Tom Pantelis <[email protected]>

.github/workflows/post-release.yml

@@ -3,16 +3,19 @@ name: Post Release
 
 on:
   workflow_dispatch:
-  push:
-    tags:
-      - 'v*.*.*'
+  release:
+    types: [published]
 
 jobs:
   update-krew:
     name: Update krew-index
     if: github.repository_owner == 'submariner-io'
     runs-on: ubuntu-latest
     steps:
+      - name: Check out the repository
+        uses: actions/checkout@9bb56186c3b09b4f86b1c65136769dd318469633
+        with:
+          fetch-depth: 0
       - name: Get the latest release tag
         run: |
           RELEASE_JSON=$(curl -L \