system/auth: remove redundant regular expression quantifier

[efd6]

What does this PR do?

Removes a redundant regular expression quantifier in the auth message grok processor.

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

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How to test this PR locally

Related issues

• Closes [system.auth] redundant wildcard in grok expression #5294

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• Start Time: 2023-02-19T21:52:52.766+0000

• Duration: 15 min 31 sec

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Test	Results
Failed	0
Passed	194
Skipped	0
Total	194

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (3/3)	💚
Files	100.0% (4/4)	💚
Classes	100.0% (4/4)	💚
Methods	60.759% (48/79)	❕
Lines	99.533% (2771/2784)	❕
Conditionals	100.0% (0/0)	💚

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

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Package system - 1.24.2 containing this change is available at https://epr.elastic.co/search?package=system