fix the size of the recv buffer in AllGather UBR test (#1564)

test/AllGatherTests.cpp

@@ -127,7 +127,7 @@ namespace RcclUnitTesting
     const int nranks = 8;
     size_t count = 2048;
     std::vector<int> sendBuff(count, 0);
-    std::vector<int> recvBuff(count, 0);
+    std::vector<int> recvBuff(nranks*count, 0);
     std::vector<int> expected(nranks*count, 0);
 
     for (int i = 0; i < count; ++i){
@@ -146,7 +146,7 @@ namespace RcclUnitTesting
     const int nranks = 8;
     size_t count = 2048;
     std::vector<int> sendBuff(count, 0);
-    std::vector<int> recvBuff(count, 0);
+    std::vector<int> recvBuff(nranks*count, 0);
     std::vector<int> expected(nranks*count, 0);
     const bool use_managed_mem = true;
     for (int i = 0; i < count; ++i){