core: fix potential race in chainIndexerTest (#22346)

Author: s1na

core/chain_indexer_test.go

@@ -18,6 +18,7 @@ package core
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"math/big"
 	"math/rand"
@@ -224,7 +225,10 @@ func (b *testChainIndexBackend) Process(ctx context.Context, header *types.Heade
 	//t.processCh <- header.Number.Uint64()
 	select {
 	case <-time.After(10 * time.Second):
-		b.t.Fatal("Unexpected call to Process")
+		b.t.Error("Unexpected call to Process")
+		// Can't use Fatal since this is not the test's goroutine.
+		// Returning error stops the chainIndexer's updateLoop
+		return errors.New("Unexpected call to Process")
 	case b.processCh <- header.Number.Uint64():
 	}
 	return nil