qa: Wait for txindex to avoid race condition

Can be verified to be necessary through adding std::this_thread::sleep_for(0.5s) at the beginning of TxIndex::CustomAppend.

test/functional/rpc_rawtransaction.py

@@ -34,6 +34,7 @@ from test_framework.util import (
     assert_equal,
     assert_greater_than,
     assert_raises_rpc_error,
+    sync_txindex,
 )
 from test_framework.wallet import (
     getnewdestination,
@@ -109,6 +110,7 @@ class RawTransactionsTest(BitcoinTestFramework):
             self.log.info(f"Test getrawtransaction {'with' if n == 0 else 'without'} -txindex")
 
             if n == 0:
+                sync_txindex(self, self.nodes[n])
                 # With -txindex.
                 # 1. valid parameters - only supply txid
                 assert_equal(self.nodes[n].getrawtransaction(txId), tx['hex'])