[AWS] Fix typo in field name causing erroneous timestamp detection on s3access

[zmoog]

What does this PR do?

Fix a small typo in a field name.

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.

[elasticmachine]

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• Start Time: 2023-05-16T08:04:12.669+0000

• Duration: 53 min 51 sec

Test stats 🧪

Test	Results
Failed	0
Passed	188
Skipped	4
Total	192

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (15/15)	💚
Files	93.75% (15/16)	👎 -6.25
Classes	93.75% (15/16)	👎 -6.25
Methods	86.131% (236/274)	👎 -13.869
Lines	85.925% (7387/8597)	👎 -7.896
Conditionals	100.0% (0/0)	💚

[elasticmachine]

Package aws - 1.35.1 containing this change is available at https://epr.elastic.co/search?package=aws

[elasticmachine]

Package aws - 1.36.8 containing this change is available at https://epr.elastic.co/search?package=aws