Hello Muhmmad
That’s a good question. It would seem that something like IGMP snooping could be used in such a case to ensure unwanted multicast traffic doesn’t reach a router like that. Although Layer 2 switches are IGMP-aware and can deal with delivering multicast traffic only to hosts that want it, they are unable to act upon PIM messages such as PIM prune in the same way, to help in making such communication more efficient.
In such a case, a network designer should choose a better topology, such as ensuring that R2 and R3 are in different network segments.
I hope this has been helpful!
Laz