Backport changes for LCG_106a / Boost 1.86
As discussed in today's GRC, backport a few include fixes to make Gaudi v38r0 compile against LCG_106a:
- gaudi/Gaudi!1587 (merged)
- gaudi/Gaudi!1618 (merged)
- One extra fix in AvalancheSchedulerSvc
@leggett can you tag this into a Gaudi v38r0.004 and update our 24.0 branch?