fix: avoid erroring if conflicting techniques are set from environment variables

[zimeg]

Summary

This PR allows both environment variables SLACK_TOKEN and SLACK_WEBHOOK_URL to exist in a workflow without causing steps to error due to an undefined technique! Fixes #373.

Reviewers

Add the following to the workflow in develop.yml before running with npm run dev:

+   env:
+     SLACK_TOKEN: ${{ secrets.SLACK_BOT_TOKEN }}
    runs-on: ubuntu-latest

This should error before the change is applied but not after!

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[seratch]

I haven't verified the behavior but the code changes look good to me and there is nothing to suggest so far. This is pretty cool!

[zimeg]

@seratch Thank you once again for such a fast review! I'll test this a few more times before merging, but will merge once things are feeling good.

Also leaving a few notes on some of the stranger changes, but am hopeful that tests cover the expected behaviors well 🙏

[zimeg]

This prevents adding both token and webhook as inputs using with while still allowing both environment variables!

[zimeg]

Special care was taken in flipping these cases with wording since we can't assume a set this.inputs.token means that technique is being used.

Instead, I think we must check for a method instead of token, and always check method before webhook 🤔

[zimeg]

IMO an important change that might've been missed without testing a bit! Before changes, an environment variable might've set this and caused this case to run despite possible inputs preferring the webhook.

This is covered and confirmed in the send.spec.js tests!

[zimeg]

🚢 💨 Merging now! But going to hold off on an immediate release with hopes of landing a few docs updates before the next tag. Planning to make those changes soon in another PR- 🫡