Update nightly mar signing key

After generating a new signing key on tbb-nightlies@tbb-nightlies-master.torproject.org, we should update nightly signing key in toolkit/mozapps/update/updater/nightly_aurora_level3_primary.der and toolkit/mozapps/update/updater/nightly_aurora_level3_secondary.der.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information