Title: Improve error handling and remove unused parameter in main.py

Description

This pull request introduces two refactoring changes to main.py aimed at improving code clarity and maintainability.

Changes

• Use specific exception for file not found
  Replace raising a general IOError with the more specific FileNotFoundError when a dotenv file is not found. This provides clearer error information and enables more precise exception handling by callers.

  Before (approx. line 377):

  if raise_error_if_not_found:
      raise IOError("File not found")
  return ""

  After:

  if raise_error_if_not_found:
      raise FileNotFoundError("File not found")
  return ""

• Remove unused parameter in main.py
  Remove the unused parameter to reduce confusion and improve function signatures. (Include the exact parameter name and small code diff in the commit if needed.)

Tests updated

• Update tests to expect the new exception type. In tests/test_main.py at line 349, change the assertion from expecting IOError to expecting FileNotFoundError.

  Before:

  with pytest.raises(IOError):
      dotenv.find_dotenv(raise_error_if_not_found=True, usecwd=True)

  After:

  with pytest.raises(FileNotFoundError):
      dotenv.find_dotenv(raise_error_if_not_found=True, usecwd=True)