Improve error handling for missing issues: write/pull-requests: write

[jsoref]

Consider a run of a workflow using this action from a fork with restricted permissions: https://github.com/check-spelling-sandbox/opentelemetry-python-contrib/actions/runs/12592914477/job/35098193103#step:2:8

component-owners/src/main.ts

Lines 49 to 55 in 58bd86e

	const addAssigneesResult = await client.rest.issues.addAssignees({
	owner: github.context.repo.owner,
	repo: github.context.repo.repo,
	issue_number: github.context.issue.number,
	assignees: Array.from(owner_users),
	});
	core.debug(util.inspect(addAssigneesResult));

Run dyladan/component-owners@main
4 owners found ofek1weiss oxeye-nikolay nikosokolik shalevr
Adding assignees
Error: Resource not accessible by integration - https://docs.github.com/rest/issues/assignees#add-assignees-to-an-issue

The readme suggests the correct permissions:

component-owners/README.md

Lines 54 to 57 in 58bd86e

	permissions:
	contents: read # to read changed files
	issues: write # to read/write issue assignees
	pull-requests: write # to read/write PR reviewers

But when a workflow doesn't correctly request them, the action should provide a better error message.