fix: fall back to next scope when no restore keys

[dulacp]

Bug

A PR workflow that restores a cache gets a miss, even when an entry with the exact same key exists on the base branch scope.

Expected: the lookup should fall back from the PR scope (refs/pull/N/merge) to the base-branch scope (refs/heads/main) and return that entry.

Impact

Every PR misses the base-branch cache and creates its own copy on first run. In one repo we observed 26 duplicate copies of the same key across PR scopes because fallback never kicked in.

Fix

Change return to continue so the loop proceeds to the next scope.

Test

No existing test covers multi-scope lookups without restore keys. Happy to add one if helpful — the current tests/e2e.test.ts uses a single scope so the bug doesn't surface there.

[kuhnroyal]

This is probably the reason my storage requirements are blowing up :)
@LouisHaftmann Can you merge and release this?