Add coverage missed reason to blake2 tests

Author: marioevz

tests/istanbul/eip152_blake2/test_blake2.py

@@ -33,6 +33,11 @@
         "https://github.com/ethereum/execution-spec-tests/pull/1244",
         "https://github.com/ethereum/execution-spec-tests/pull/1067",
     ],
+    coverage_missed_reason=(
+        "No longer used opcodes, SUB, GT, ISZERO, AND, CODESIZE, JUMP, some PUSH opcodes."
+        "Original test calls Blake2b in ConstantinopleFix (activation test), "
+        "which results in empty account code being triggered."
+    ),
 )
 @pytest.mark.valid_from("Istanbul")
 @pytest.mark.parametrize("call_opcode", [Op.CALL])