misc: Add 'synchronize' as CI Test action. Remove 'reopen'

'synchronize' will re-run the tests everytime the pull-request is
updated, inclusive of rebasing. 'reopen' seems pointless as reopening
does not change the pull-request functionality.

Change-Id: I24c2686e19a8b0901323e9bd794142994dc2a87c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/71503
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed