[o365] pipeline bug fix

[leehinman]

What does this PR do?

Fixes processing of ModifiedProperties when it is a list of strings
instead of a list of objects

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.

How to test this PR locally

elastic-package stack up -d
eval "$(elastic-package stack shellinit)"
elastic-package test
elastic-package stack down

[elasticmachine]

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

[elasticmachine]

💚 Build Succeeded

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Build stats

• Start Time: 2022-04-26T20:46:35.223+0000

• Duration: 12 min 26 sec

Test stats 🧪

Test	Results
Failed	0
Passed	29
Skipped	0
Total	29

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[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	100.0% (1/1)	💚 2.918
Classes	100.0% (1/1)	💚 2.918
Methods	100.0% (15/15)	💚 12.106
Lines	80.704% (665/824)	👎 -7.975
Conditionals	100.0% (0/0)	💚

[P1llus]

LGTM