Extract bench according to wiki instructions

- loop through the commits starting from the latest one
- read the bench value from the last match, if any, of the template
  in the commit body text

closes https://github.com/official-stockfish/Stockfish/pull/4627

No functional change

.github/workflows/stockfish_test.yml

@@ -103,6 +103,10 @@ jobs:
             echo "ANDROID_NDK_BIN=$ANDROID_NDK_BIN" >> $GITHUB_ENV
           fi
 
+      - name: Download required macOS packages
+        if: runner.os == 'macOS'
+        run: brew install coreutils
+
       - name: Setup msys and install required packages
         if: runner.os == 'Windows'
         uses: msys2/setup-msys2@v2
@@ -115,8 +119,10 @@ jobs:
 
       - name: Extract the bench number from the commit history
         run: |
-          benchref=$(git log HEAD | grep -m 1 -o -x "[[:space:]]*\b[Bb]ench[ :]\+[1-9][0-9]\{5,7\}\b[[:space:]]*" | sed "s/[^0-9]//g") || true
+          for ((n=0; n<100; n++)); do
-          [[ -n "$benchref" ]] && echo "benchref=$benchref" >> $GITHUB_ENV && echo "Reference bench: $benchref" || echo "No bench found"
+            benchref=$(git log HEAD~$n -1 | tac | grep -m 1 -o -x '[[:space:]]*\b[Bb]ench[ :]\+[1-9][0-9]\{5,7\}\b[[:space:]]*' | sed 's/[^0-9]//g') && break || true
+          done
+          [[ -n "$benchref" ]] && echo "benchref=$benchref" >> $GITHUB_ENV && echo "From commit: $(git rev-parse HEAD~$n)" && echo "Reference bench: $benchref" || echo "No bench found"
 
       - name: Check compiler
         run: |