Tweak ttCapture reduction

More reduction at shallow depth for quiet moves when ttMove is a capture.

Passed STC:
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 365728 W: 95896 L: 95090 D: 174742
Ptnml(0-2): 1283, 43133, 93262, 43867, 1319
https://tests.stockfishchess.org/tests/view/66edd35986d5ee47d953b0d5

Passed LTC:
LLR: 2.96 (-2.94,2.94) <0.50,2.50>
Total: 200526 W: 51197 L: 50540 D: 98789
Ptnml(0-2): 119, 21952, 55462, 22613, 117
https://tests.stockfishchess.org/tests/view/66f405dc86d5ee47d953b460

closes official-stockfish#5610

bench: 1269487

src/search.cpp

@@ -1157,7 +1157,7 @@ Value Search::Worker::search(
 
         // Increase reduction if ttMove is a capture but the current move is not a capture (~3 Elo)
         if (ttCapture && !capture)
-            r++;
+            r += 1 + (depth < 8);
 
         // Increase reduction if next ply has a lot of fail high (~5 Elo)
         if ((ss + 1)->cutoffCnt > 3)