[chore][exporter/otlphttpexporter] Enable goleak check (#9222)

**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.-->
Enables goleak checks against all tests for the otlphttpexporter. This
is the exact same change done in #9210 I just missed it in that change.

**Link to tracking Issue:** <Issue number if applicable>
#9165

**Testing:** <Describe what testing was performed and which tests were
added.>
All tests are passing.

exporter/otlphttpexporter/go.mod

@@ -17,6 +17,7 @@ require (
 	go.opentelemetry.io/collector/pdata v1.0.0
 	go.opentelemetry.io/otel/metric v1.21.0
 	go.opentelemetry.io/otel/trace v1.21.0
+	go.uber.org/goleak v1.3.0
 	go.uber.org/zap v1.26.0
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20231127180814-3a041ad873d4
 	google.golang.org/grpc v1.60.1

exporter/otlphttpexporter/package_test.go

@@ -0,0 +1,17 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package otlphttpexporter
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+// The IgnoreTopFunction call prevents catching the leak generated by opencensus
+// defaultWorker.Start which at this time is part of the package's init call.
+// See https://github.com/open-telemetry/opentelemetry-collector/issues/9165#issuecomment-1874836336 for more context.
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m, goleak.IgnoreTopFunction("go.opencensus.io/stats/view.(*worker).start"))
+}