Data race in IMC dispatcher

[vaikas]

Describe the bug
From:
https://prow.knative.dev/view/gcs/knative-prow/logs/ci-knative-eventing-continuous/1299329237383122944

==================
WARNING: DATA RACE
Read at 0x00c0005e8ee3 by goroutine 55:
  testing.(*common).logDepth()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:710 +0xa7
  testing.(*common).log()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:703 +0x8f
  testing.(*common).Logf()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:749 +0x21
  testing.(*T).Logf()
      <autogenerated>:1 +0x75
  go.uber.org/zap/zaptest.testingWriter.Write()
      /home/prow/go/src/knative.dev/eventing/vendor/go.uber.org/zap/zaptest/logger.go:130 +0x11f
  go.uber.org/zap/zaptest.(*testingWriter).Write()
      <autogenerated>:1 +0xa9
  go.uber.org/zap/zapcore.(*ioCore).Write()
      /home/prow/go/src/knative.dev/eventing/vendor/go.uber.org/zap/zapcore/core.go:90 +0x1c3
  go.uber.org/zap/zapcore.(*CheckedEntry).Write()
      /home/prow/go/src/knative.dev/eventing/vendor/go.uber.org/zap/zapcore/entry.go:216 +0x1e7
  go.uber.org/zap.(*SugaredLogger).log()
      /home/prow/go/src/knative.dev/eventing/vendor/go.uber.org/zap/sugar.go:234 +0x141
  go.uber.org/zap.(*SugaredLogger).Errorw()
      /home/prow/go/src/knative.dev/eventing/vendor/go.uber.org/zap/sugar.go:191 +0x27a
  knative.dev/eventing/pkg/reconciler/inmemorychannel/dispatcher.NewController.func3()
      /home/prow/go/src/knative.dev/eventing/pkg/reconciler/inmemorychannel/dispatcher/controller.go:110 +0xf3

Previous write at 0x00c0005e8ee3 by goroutine 46:
  testing.tRunner.func1()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:1025 +0x467
  testing.tRunner()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:1043 +0x20d

Goroutine 55 (running) created at:
  knative.dev/eventing/pkg/reconciler/inmemorychannel/dispatcher.NewController()
      /home/prow/go/src/knative.dev/eventing/pkg/reconciler/inmemorychannel/dispatcher/controller.go:107 +0x1408
  knative.dev/eventing/pkg/reconciler/inmemorychannel/dispatcher.TestNewInNamespace()
      /home/prow/go/src/knative.dev/eventing/pkg/reconciler/inmemorychannel/dispatcher/controller_test.go:47 +0x111
  testing.tRunner()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:1039 +0x1eb

Goroutine 46 (running) created at:
  testing.(*T).Run()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:1090 +0x700
  testing.runTests.func1()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:1334 +0xa6
  testing.tRunner()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:1039 +0x1eb
  testing.runTests()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:1332 +0x527
  testing.(*M).Run()
      /root/.gvm/gos/go1.14.6/src/testing/testing.go:1249 +0x43f
  main.main()
      _testmain.go:48 +0x223
==================

Expected behavior
Not that

To Reproduce
Steps to reproduce the behavior.

Knative release version

Additional context
Add any other context about the problem here such as proposed priority

[slinkydeveloper]

/assign