gcs-mock-service: fix bucket created once per file instead of once per bucket

[efd6]

Proposed commit message

gcs-mock-service: fix bucket created once per file instead of once per bucket

processManifest called createBucket inside the per-file loop, so any
bucket configured with more than one file would fail on the second file
with "bucket already exists" and exit with code 1. Move the call outside
the inner loop so the bucket is created once per bucket entry.

Note

No changelogs since this is not user-facing.

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.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• For netskope: add script test for routing rules #20455

Screenshots

[infra-vault-gh-plugin-prod]

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• Commit: 1c0d568

cc @efd6

[infra-vault-gh-plugin-prod]

Pinging @elastic/security-service-integrations (Team:Security-Service Integrations)

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[ShourieG]

LGTM, thanks for this fix.