Keep workflow running even if no release tag found

The action we used to delete the old release somehow cannot find the
release tag in forked repo and cause the workflow failed.
To solve this issue, simply setting `fail-if-no-release` option to false
will do the trick.

.github/workflows/generate_doc.yaml

@@ -23,6 +23,7 @@ jobs:
  with:
  token: ${{ github.token }}
  fail-if-no-assets: false
+ fail-if-no-release: false
  tag: latest
  assets: |
  lkmpg.pdf