fix(general): fix lazy loading custom policies into check registry

[mikeurbanski1]

User description

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Description

Fixes an issue preventing custom policies from running.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my feature, policy, or fix is effective and works
• New and existing tests pass locally with my changes

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Generated description

Dear maintainer, below is a concise technical summary of the changes proposed in this PR:

Fix an issue in the Registry class that prevents custom policies from being loaded into the check registry. Modify the load_checks method to ensure custom policies are added only once and introduce a flag custom_policies_loaded to track the loading status.

Topic	Details
Custom Policy Loading	Fix the lazy loading mechanism for custom policies in the Registry class. Modified files (1) checkov/common/checks_infra/registry.py Latest Contributors(2) Email Commit Date iifrach@paloaltonetwor... feat-general-Support-m... August 18, 2024 123508988+taviassaf@us... feat-general-support-m... August 05, 2024

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