fix(test_scanner.py): Add test for unopenable file condition

[JigyasuRajput]

Description

Fixes #762

• Introduces a new test to cover scenarios where a file exists but cannot be opened (e.g., due to permission issues).
• Complements the existing test for non-existent files, enhancing overall error handling coverage.

Changes

• New Test: test_unopenable_file
  • Creates a temporary file and forces an OSError (simulating a permission error) using unittest.mock.patch.
  • Asserts that the scan_file function handles the error by raising a StopIteration.
• Existing Test: test_cannot_open_file
  • Continues to validate behavior when a file does not exist and ensures proper logging of an "Invalid file" message.

Testing

• Purpose:
  • Ensures that the scanner behaves correctly in both scenarios:
    • Non-existent file.
    • File exists but is unopenable due to permissions.
• Expected Outcome:
  • Both tests should raise a StopIteration, confirming that the error handling in scanner.py is robust.

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Additional Context

• This addition improves the reliability of file scanning by explicitly testing error conditions that were previously unverified.
• It addresses the gap highlighted in issue [#762](Add test for "unopenable file" condition in scanner.py #762).