test: sync access to countRun counter in TestRunnerFactory

[kruskall]

Proposed commit message

countRun is incremented and checked in different goroutines

to avoid race conditions, only mark the workgroup as done after incrementing the counter

==================
WARNING: DATA RACE
Read at 0x00c000358fc8 by goroutine 10:
  github.com/elastic/beats/v7/filebeat/input/v2/compat.TestRunnerFactory_CheckConfig.func2()
      github.com/elastic/beats/v7/filebeat/input/v2/compat/compat_test.go:127 +0xa31
  testing.tRunner()
      testing/testing.go:1690 +0x226
  testing.(*T).Run.gowrap1()
      testing/testing.go:1743 +0x44

Previous write at 0x00c000358fc8 by goroutine 14:
  github.com/elastic/beats/v7/filebeat/input/v2/compat.TestRunnerFactory_CheckConfig.func2.1.2()
      github.com/elastic/beats/v7/filebeat/input/v2/compat/compat_test.go:89 +0x4f
  github.com/elastic/beats/v7/filebeat/input/v2/internal/inputest.(*MockInput).Run()
      github.com/elastic/beats/v7/filebeat/input/v2/internal/inputest/inputest.go:80 +0x124
  github.com/elastic/beats/v7/filebeat/input/v2/compat.(*runner).Start.func1()
      github.com/elastic/beats/v7/filebeat/input/v2/compat/compat.go:136 +0x3c7

Goroutine 10 (running) created at:
  testing.(*T).Run()
      testing/testing.go:1743 +0x825
  github.com/elastic/beats/v7/filebeat/input/v2/compat.TestRunnerFactory_CheckConfig()
      github.com/elastic/beats/v7/filebeat/input/v2/compat/compat_test.go:67 +0x56
  testing.tRunner()
      testing/testing.go:1690 +0x226
  testing.(*T).Run.gowrap1()
      testing/testing.go:1743 +0x44

Goroutine 14 (finished) created at:
  github.com/elastic/beats/v7/filebeat/input/v2/compat.(*runner).Start()
      github.com/elastic/beats/v7/filebeat/input/v2/compat/compat.go:133 +0x16f
  github.com/elastic/beats/v7/filebeat/input/v2/compat.TestRunnerFactory_CheckConfig.func2()
      github.com/elastic/beats/v7/filebeat/input/v2/compat/compat_test.go:116 +0x7a9
  testing.tRunner()
      testing/testing.go:1690 +0x226
  testing.(*T).Run.gowrap1()
      testing/testing.go:1743 +0x44
==================
--- FAIL: TestRunnerFactory_CheckConfig (0.00s)
    --- FAIL: TestRunnerFactory_CheckConfig/does_not_cause_input_ID_duplication (0.00s)
        testing.go:1399: race detected during execution of test

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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[botelastic]

This pull request doesn't have a Team:<team> label.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @kruskall? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.