[ci] Schedule CIRCT Nightly +2 hours later

Change the time that the CIRCT nightly runs from 0800 UTC to 1000 UTC.
This increase the staggering between the upstream llvm/circt nightly
artifact job from a 1-hour delay to a 3-hour delay (start time to start
time).  The upstream llvm/circt nightly artifact job is now longer (~2.5
hours) as it builds full CIRCT w/ shared libs as opposed to just firtool.

This avoids a "bug" where the Chisel/CIRCT nightly would run before the
CIRCT artifact nightly finished causing the former to use the previous
night's nightly.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>