lambda-promtail-: fix parse kinesis timestamp

[lfelipevaca]

What this PR does / why we need it:

Which issue(s) this PR fixes: Fixes #

Special notes for your reviewer:

Checklist

• [x] Documentation added
• [x] Tests updated
• [ ] Is this an important fix or new feature? Add an entry in the CHANGELOG.md.
• [ ] Changes that require user attention or interaction to upgrade are documented in docs/sources/upgrading/_index.md

[CLAassistant]

All committers have signed the CLA.

[lfelipevaca]

this change solves the problem described in the following issue

https://github.com/grafana/loki/issues/7159

[grafanabot]

./tools/diff_coverage.sh ../loki-main/test_results.txt test_results.txt ingester,distributor,querier,querier/queryrange,iter,storage,chunkenc,logql,loki

Change in test coverage per package. Green indicates 0 or positive change, red indicates that test coverage for a package fell.

+           ingester	0%
+        distributor	0%
+            querier	0%
+ querier/queryrange	0%
+               iter	0%
+            storage	0%
+           chunkenc	0%
+              logql	0%
+               loki	0%

[stale[bot]]

Hi! This issue has been automatically marked as stale because it has not had any activity in the past 30 days.

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[MichelHollands]

@lfelipevaca Thanks for this contribution. There is a unit test for parsing Kinesis events. Can you add a check for this change?