GoogleAnalytics: Added unit test for order success observer

[rogyar]

Description

This PR adds missing unit test for Magento\GoogleAnalytics\Observer\SetGoogleAnalyticsOnOrderSuccessPageViewObserver class

Fixed Issues (if relevant)

N/A

Manual testing scenarios

N/A

[magento-engcom-team]

Hi @rogyar. Thank you for your contribution
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[magento-engcom-team]

Hi @rogyar. Thank you for your contribution.
We will aim to release these changes as part of 2.2.6.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.

[magento-engcom-team]

Hi @rogyar. Thank you for your contribution.
We will aim to release these changes as part of 2.2.6.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.