Decrease probCutBeta based on opponentWorsening

Passed STC:
LLR: 2.97 (-2.94,2.94) <0.00,2.00>
Total: 62112 W: 16305 L: 15947 D: 29860
Ptnml(0-2): 203, 7226, 15856, 7552, 219
https://tests.stockfishchess.org/tests/view/66f85fc986d5ee47d953b71e

Passed LTC:
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 129552 W: 33223 L: 32710 D: 63619
Ptnml(0-2): 94, 14250, 35573, 14767, 92
https://tests.stockfishchess.org/tests/view/66f93fef86d5ee47d953b7d2

closes official-stockfish#5615

bench: 1511354

src/search.cpp

@@ -840,7 +840,7 @@ Value Search::Worker::search(
     // Step 11. ProbCut (~10 Elo)
     // If we have a good enough capture (or queen promotion) and a reduced search
     // returns a value much above beta, we can (almost) safely prune the previous move.
-    probCutBeta = beta + 189 - 53 * improving;
+    probCutBeta = beta + 189 - 53 * improving - 30 * opponentWorsening;
     if (!PvNode && depth > 3
         && std::abs(beta) < VALUE_TB_WIN_IN_MAX_PLY
         // If value from transposition table is lower than probCutBeta, don't attempt