feat: filter out nil actions in action waiter

[jooola]

Filter out nil actions, to help users of the function.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 70.92%. Comparing base (895ada1) to head (1bfcdbc).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #464 +/- ## ======================================= Coverage 70.91% 70.92% ======================================= Files 36 36 Lines 3799 3800 +1 ======================================= + Hits 2694 2695 +1 Misses 692 692 Partials 413 413 ```

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[github-actions[bot]]

The backport to release-1.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release-1.x release-1.x
# Navigate to the new working tree
cd .worktrees/backport-release-1.x
# Create a new branch
git switch --create backport-464-to-release-1.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 4fc9a4039d45071124a435121642ca396a8237c0
# Push it to GitHub
git push --set-upstream origin backport-464-to-release-1.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-1.x

Then, create a pull request where the base branch is release-1.x and the compare/head branch is backport-464-to-release-1.x.