refactor: test: use _ variable for unused loop counters

substitutes "for x in range(N):" by "for _ in range(N):"
indicates to the reader that a block is just repeated N times, and
that the loop counter is not used in the body

test/functional/feature_csv_activation.py

@@ -161,7 +161,7 @@ class BIP68_112_113Test(BitcoinTestFramework):
 
     def generate_blocks(self, number):
         test_blocks = []
-        for i in range(number):
+        for _ in range(number):
             block = self.create_test_block([])
             test_blocks.append(block)
             self.last_block_time += 600
@@ -209,22 +209,22 @@ class BIP68_112_113Test(BitcoinTestFramework):
         # Note we reuse inputs for v1 and v2 txs so must test these separately
         # 16 normal inputs
         bip68inputs = []
-        for i in range(16):
+        for _ in range(16):
             bip68inputs.append(send_generic_input_tx(self.nodes[0], self.coinbase_blocks, self.nodeaddress))
 
         # 2 sets of 16 inputs with 10 OP_CSV OP_DROP (actually will be prepended to spending scriptSig)
         bip112basicinputs = []
-        for j in range(2):
+        for _ in range(2):
             inputs = []
-            for i in range(16):
+            for _ in range(16):
                 inputs.append(send_generic_input_tx(self.nodes[0], self.coinbase_blocks, self.nodeaddress))
             bip112basicinputs.append(inputs)
 
         # 2 sets of 16 varied inputs with (relative_lock_time) OP_CSV OP_DROP (actually will be prepended to spending scriptSig)
         bip112diverseinputs = []
-        for j in range(2):
+        for _ in range(2):
             inputs = []
-            for i in range(16):
+            for _ in range(16):
                 inputs.append(send_generic_input_tx(self.nodes[0], self.coinbase_blocks, self.nodeaddress))
             bip112diverseinputs.append(inputs)