test: use f-strings in mining_*.py tests

Author: fanquake

test/functional/mining_basic.py

@@ -65,10 +65,10 @@ def mine_chain(self):
         assert_equal(mining_info['currentblockweight'], 4000)
 
         self.log.info('test blockversion')
-        self.restart_node(0, extra_args=['-mocktime={}'.format(t), '-blockversion=1337'])
+        self.restart_node(0, extra_args=[f'-mocktime={t}', '-blockversion=1337'])
         self.connect_nodes(0, 1)
         assert_equal(1337, self.nodes[0].getblocktemplate(NORMAL_GBT_REQUEST_PARAMS)['version'])
-        self.restart_node(0, extra_args=['-mocktime={}'.format(t)])
+        self.restart_node(0, extra_args=[f'-mocktime={t}'])
         self.connect_nodes(0, 1)
         assert_equal(VERSIONBITS_TOP_BITS + (1 << VERSIONBITS_DEPLOYMENT_TESTDUMMY_BIT), self.nodes[0].getblocktemplate(NORMAL_GBT_REQUEST_PARAMS)['version'])
         self.restart_node(0)