[Security] Refactor gitMutex key naming in chaoscenter/graphql/server/pkg/gitops/git-lock.go

[ParkChangSun]

Proposed changes

Changed the variable name "key" in function Lock & Unlock in chaoscenter/graphql/server/pkg/gitops/git-lock.go into "url".

Types of changes

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• New feature (non-breaking change which adds functionality)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices applies)

Checklist

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• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added necessary documentation (if appropriate)

Dependency

N/A

Special notes for your reviewer:

[namkyu1999]

This pr solved below security issues

• https://github.com/litmuschaos/litmus/security/code-scanning/87
• https://github.com/litmuschaos/litmus/security/code-scanning/86