Fix flaxy 0003-block-building-warp-sync test (#8882)

Fixes: #8868

The error skipped in log is acceptable, the announced block does not
have the parent imported yet.

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Co-authored-by: cmd[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: 2 people

prdoc/pr_8882.prdoc

@@ -0,0 +1,8 @@
+title: Fix flaxy `0003-block-building-warp-sync` test
+doc:
+- audience: Node Dev
+  description: |-
+    Fixes: https://github.com/paritytech/polkadot-sdk/issues/8868
+
+    The error skipped in log is acceptable, the announced block does not have the parent imported yet.
+crates: []

substrate/zombienet/0003-block-building-warp-sync/test-block-building-warp-sync.zndsl

@@ -34,5 +34,6 @@ dave: log line matches "Block history download is complete" within 10 seconds
 dave: reports substrate_beefy_best_block is at least {{DB_BLOCK_HEIGHT}} within 180 seconds
 dave: reports substrate_beefy_best_block is greater than {{DB_BLOCK_HEIGHT}} within 60 seconds
 
-dave: count of log lines containing "error" is 0 within 10 seconds
+# The block history download runs in the background while the fresh blocks are imported. This error can pop out in the log and is acceptable: the freshly announced block may not have the parent imported yet.
+dave: count of log lines containing "error(?! importing block .*: block has an unknown parent)" is 0 within 10 seconds
 dave: count of log lines containing "verification failed" is 0 within 10 seconds