ci: Only run mobile jobs in the Envoy repo

[phlax]

Signed-off-by: Ryan Northey ryan@synca.io

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[phlax]

cc @jpsim this is fairly urgent as mirror repos are trying to run all of the mobile tests and failing

the solution is far from ideal - having to exclude at the job level - after trawling through the docs and design decisions here i have come to the firm conclusion that github/ms' intention is to trigger as much unwanted CI as they can get away with

[jpsim]

+1 to unblock, however we should consider doing the same for the other GitHub Actions CI jobs like CodeQL.

Also, do we have something similar in place for the Azure Pipelines CI?

[phlax]

i think we do this already for ~all of the existing gh jobs - in the case of azp we want them to run in current mirror

[phlax]

... in the case of azp we want them to run in current mirror

so actually this is slightly more complex - azp has to be setup for a repo for it to trigger at all - so i think the file is harmless if that is not set up, and ~needed if it is

fwiw, triggers in the file are mostly ignored in favour of web config even where it is set up