ci(main): upgrade actions/checkout to v3
To be up to date with actions/checkout opens the door to use the latest
features if necessary and get the latest security patches.
This also avoids a couple of deprecation warnings in the CI runs.
Note: The `actions/checkout` Action has been known to be broken in i686
containers as of v2, therefore we keep forcing it to v1 there. See
actions/runner#2115 for more details.
Signed-off-by: Oscar Dominguez <dominguez.celada@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>