[chore][pkg/stanza/operator/transformer/recombine] Enable goleak check (

#31095)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
This enables `goleak` checks on the
`pkg/stanza/operator/transformer/recombine` package, to help ensure no
goroutines are leaking. This is a test only change, adding a missing
`Stop` call, as well as stopping a running goroutine in a test.

**Link to tracking Issue:** <Issue number if applicable>
#30438

**Testing:** <Describe what testing was performed and which tests were
added.>
All existing tests are passing, as well as added `goleak` check.

---------

Co-authored-by: Daniel Jaglowski <jaglows3@gmail.com>

pkg/stanza/operator/transformer/recombine/package_test.go

@@ -0,0 +1,14 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package recombine
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}

pkg/stanza/operator/transformer/recombine/recombine_test.go

@@ -504,6 +504,7 @@ func TestTransformer(t *testing.T) {
 			op, err := tc.config.Build(testutil.Logger(t))
 			require.NoError(t, err)
 			require.NoError(t, op.Start(testutil.NewUnscopedMockPersister()))
+			defer func() { require.NoError(t, op.Stop()) }()
 			recombine := op.(*Transformer)
 
 			fake := testutil.NewFakeOutput(t)
@@ -709,13 +710,21 @@ func TestTimeoutWhenAggregationKeepHappen(t *testing.T) {
 	require.NoError(t, recombine.Start(nil))
 	require.NoError(t, recombine.Process(ctx, e))
 
+	done := make(chan struct{})
+	ticker := time.NewTicker(cfg.ForceFlushTimeout / 2)
 	go func() {
 		next := entry.New()
 		next.Timestamp = time.Now()
 		next.Body = "next"
 		for {
-			time.Sleep(cfg.ForceFlushTimeout / 2)
-			require.NoError(t, recombine.Process(ctx, next))
+			select {
+			case <-done:
+				ticker.Stop()
+				return
+			case <-ticker.C:
+				require.NoError(t, recombine.Process(ctx, next))
+
+			}
 		}
 	}()
 
@@ -726,6 +735,7 @@ func TestTimeoutWhenAggregationKeepHappen(t *testing.T) {
 		t.FailNow()
 	}
 	require.NoError(t, recombine.Stop())
+	close(done)
 }
 
 func TestSourceBatchDelete(t *testing.T) {