system/security: add test cases for events 4738 and 4742

[efd6]

What does this PR do?

This adds test cases for events 4738 and 4742, missed in the original bugfix.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Updates Error in System integration  #3898

Screenshots

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[elasticmachine]

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Build stats

• Start Time: 2022-08-22T05:10:09.472+0000

• Duration: 16 min 13 sec

Test stats 🧪

Test	Results
Failed	0
Passed	273
Skipped	0
Total	273

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (3/3)	💚
Files	100.0% (4/4)	💚 2.913
Classes	100.0% (4/4)	💚 2.913
Methods	60.759% (48/79)	👎 -28.843
Lines	98.793% (2702/2735)	👍 7.054
Conditionals	100.0% (0/0)	💚

[andrewkroh]

👍

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[leehinman]

LGTM