ci: renovate fails for forks

[kkourt]

Renovate action fails for forked tetragon repos. This can be annoying for external developers, especially since the action is run periodically.
Maybe there is a way to constrain the action to be run only on cilium/tetragon?

Example failure from kkourt/tetragon (https://github.com/kkourt/tetragon/actions/runs/11821115027/job/32935072459):

Get token:
Traceback (most recent call last):
  File "/app/token_getter.py", line 143, in <module>
    assert app_id, 'Must supply input APP_ID'
AssertionError: Must supply input APP_ID