test: Avoid F541 (f-string without any placeholders)

test/functional/feature_loadblock.py

@@ -51,8 +51,8 @@ class LoadblockTest(BitcoinTestFramework):
             cfg.write(f"port={node_url.port}\n")
             cfg.write(f"host={node_url.hostname}\n")
             cfg.write(f"output_file={bootstrap_file}\n")
-            cfg.write(f"max_height=100\n")
-            cfg.write(f"netmagic=fabfb5da\n")
+            cfg.write("max_height=100\n")
+            cfg.write("netmagic=fabfb5da\n")
             cfg.write(f"input={blocks_dir}\n")
             cfg.write(f"genesis={genesis_block}\n")
             cfg.write(f"hashlist={hash_list.name}\n")