syz-manager: check git revision on start
syz-manager: check git revision on start

If we have no git revision, we will fail later anyway.
Better to fail earlier.

xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,zoulasc/syzkaller,google/syzkaller,zoulasc/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,zoulasc/syzkaller,xairy/syzkaller,zoulasc/syzkaller