github-token should use token from context as a default fallback

[polarathene]

actions-netlify/action.yml

Lines 14 to 16 in f242d4c

	github-token:
	description: GitHub token
	required: false

github-token could source the token from context as default. Here's an example of an action doing that.

It's not communicated via action logs or README, but if you attempt to use any features of the action that require the token, they'll silently "fail" by being skipped if that token is missing/empty:

actions-netlify/src/main.ts

Lines 127 to 131 in f242d4c

	// Get GitHub token
	const githubToken = inputs.githubToken()
	if (githubToken === '') {
	return
	}

---

Likewise, with permissions being restricted, these features of the action will need specific permissions granted. It'd be worthwhile to document them on the README.