ignore: add mino_opcounts to gitignore

The MINO_BC_OP_COUNTS=1 build (v0.157.1) produces a `mino_opcounts`
binary alongside the existing mino_prof / mino_asan / mino_ubsan
specialized builds; ignore it the same way.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: leifericf

.gitignore

@@ -14,6 +14,7 @@ bin/
 /mino_tsan
 /mino_ubsan
 /mino_prof
+/mino_opcounts
 /data/
 src/core_mino.h
 src/lib_clojure_*.h