Fix gc-too-slow issue

Previously, with a finite set of keys, latest_extant_version could fall all the way behind so that a call to addWrites would have to do O(n) work eventually.

ConflictSet.cpp

@@ -4412,6 +4412,9 @@ struct __attribute__((visibility("hidden"))) ConflictSet::Impl {
     assert(writeContext.accum.entries_erased == 0);
     assert(writeContext.accum.entries_inserted == 0);
 
+    // Queue up some gc work just for (potentially) increasing the version
+    ++keyUpdates;
+
     if (oldestExtantVersion < writeVersion - kMaxCorrectVersionWindow)
         [[unlikely]] {
       if (writeVersion > newestVersionFullPrecision + kNominalVersionWindow) {